Reflow Oven

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Owning high temperature control system, the temperature control accuracy is within ±1℃ and deviation is within ±2℃.

Check below 4 types of Reflow oven and the definite guide to help you understand how to use it efficiently.

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Basic Description – Reflow Oven Solution From Us

ElectronicsTalk can provide various of lead-free reflow oven that has a high-standard and stability of production performance.

There are options for chain, mesh, and the two combination, which has a normal transmission speed of 1,500 mm/min. Owning to the precise temperature control system, temperature control accuracy is within ±1℃ and temperature deviation is within ±2℃.

And, Adopting the latest technologies to reach the high-efficiency: a nitrogen concentration range of 50 – 200 PPM (option), maximum cooling length of 1100mm, and maximum heating length of 4560mm.

Learning Has No Limits

ElectronicsTalk aware of this philosophy all the time, like the over 2 decades we are still serving countless individual for their PCB assebly business, check the guide we prepared here for Reflow Oven.

Learn The Knowledge

1. What is A Reflow Soldering oven?

1.1 Background & Definition

A Reflow oven is a machine used primarily for Reflow soldering of surface mount electronic components to printed circuit boards (PCB).

Generally, it is used in the assembly of a hybrid integrated circuit board. Most of the components are chip capacitor, chip inductor, mount transistor, and two-transistor.

1.2 Working Principle

As one of the three main machines in the SMT line. It working principle is as the following:

Always, it locates after the pick and place machine, and solders the PCB board and component with heating and melting, at last cool the solder to link the PCB board and component together.

With the development of SMT technology and the emergence of SMC and SMD, Reflow soldering technology and equipment as parts of SMT technology have been developed accordingly, and its application has become more and more extensive, almost in all electronics product fields.

Technically, Reflow is to realize the mechanical and electrical connection between the solder end or pin of the surface assembly component and the PCB pad by remelting the paste solder allocated to the PCB pad in advance.

Reflow soldering relies on the effect of hot airflow on the solder joint, and the soldering flux reacts physically under the fixed constant excessive temperature air go with the drift to reap to achieve SMD welding;

Therefore, it is called “reflow soldering”, because the gas circulates in the welder to generate high temperature to achieve the welding purpose.

1.3 Working Process

Reflow oven soldering process

  1. When the PCB enters the heating zone, the solvent and fuel are inside the solder paste evaporate. At the same time, the flux in the solder paste moistens the pad, component end, and pin. The solder paste softens, collapses, and covers the pad, isolating the pad and component pin from oxygen.
  2. When PCB enters the insulation area, the PCB and components are fully preheated to prevent PCB and components from being damaged due to PCB suddenly entering the welding high-temperature area.
  3. When the PCB enters the welding area, the temperature rises hastily to make the solder paste melt. The liquid solder can wet, diffuse, diffuse or reflow the solder pad, component end and pin of PCB to form a solder joint.
  4. PCB enters into the cooling area to solidify the solder joint; reflow welding is completed.

1.4 Types of the Reflow soldering oven

  • Types base on the zones

Usually, the length for each soldering zone is about 45-50cm, the quantity for the soldering zone is from three to fifteen or even more.

Furthermore, for the function of the soldering zone, reflow welding has at least three temperature zones, namely the preheating zone, welding zone and cooling zone.

Many usually exclude the cooling zone when calculating the temperature zone, that is, only the heating zone, heat preservation zone, and welding zone.

  • Types base on the working technology

There are many types of reflow soldering oven according to different working technology, but we just list three main types among it in the following, please have a look:

  • Convection reflow oven
  • Nitrogen reflow oven
  • Infrared reflow oven
  • Types base on the Shape

①Bench type reflow oven is suitable for small and medium-sized PCB assembly production with stable performance and economic price of highly flexible production arrangement.

②Vertical reflow soldering oven is applicable for different kinds of production demands, especially for mass production.

2. Infrared reflow oven VS Convection reflow oven VS Nitrogen reflow oven

So, What is the difference between these kinds of reflow oven?

2.1 Definition

  • The Infrared reflow oven:

Infrared reflow oven usually is small-sized. Its working principle is that 80% of the heat energy is emitted in the form of electromagnetic wave – infrared ray, the temperature of solder joints increases after infrared radiation, then complete the welding process.

IR reflow oven working principle

We can describe its progressive division as near-infrared ray (0.72-1.5 μ m), mid-infrared ray (1.5-5.6 μ m), far infrared ray (5.6-1000 μ m).

Conformal-Coating-Page_Infrared-Curving-Oven
Infrared reflow oven – Click here to looking more info
  • Convection reflow oven:

Nowadays, forced convection reflow is the desired technique of SMT reflow soldering of surface mounted components to a printed circuit board (PCB), and you could found the method regarding how to wrok as the below image shown.

Convention reflow oven working principle

The oven is generally separated into zones where every sector independently managed to optimize the thermal profile of the procedure sector of the oven.

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Convection reflow oven 10 Zones – Click to explore it

  • Nitrogen reflow oven

The nitrogen reflow oven has one distinct feature, during the production it is to fill nitrogen inside the oven.

Why do you like this?

The purpose is to prevent air from entering the reflow furnace and prevent the oxidation of component feet in reflow welding.

Especially, nitrogen reflow welding is mainly to enhance the welding quality, so that the welding occurs in the environment with little oxygen content (100 ppm), which can avoid the oxidation of components.

Therefore, we should pay attention to ensure that the lower the oxygen content during the production.

2.2 Advantage and disadvantage

  • Advantage and disadvantage of the Infrared reflow oven:

Each coin has two sides, hence, the infrared reflow oven also has both advantages and disadvantages, please check the details in the following contents.

Just as its name implies, infrared reflow oven uses infrared ray as its heating source

Advantages: continuous, good heating effect, wide adjustable temperature range, less solder spatter, less reflow soldering and continuous welding;

Disadvantages: Different materials on the circuit board lead to different heat absorption and difficult temperature control. Also the color of the material will affect the heating effect a lot and lead the gap of the difficult temperature control.

  • Advantage and disadvantage of the convection reflow oven:

High temperature air circulates in the reflow oven.

Advantages: hot air reflow welding heating uniform, easy to control the temperature;

Disadvantages: it is easy to cause oxidation of components, and strong wind may cause displacement of components.

  • Advantage and disadvantage of the nitrogen reflow oven:

Advantages:

① greatly prevent the reduction of oxidation during component welding

②improve the wetting force and speed up the wetting speed

③can reduce the production of solder balls, avoid bridging, and achieve higher welding quality

Disadvantages:

①high price for nitrogen, terrible for the environment.

②Increase the chance of tombstones

③Enhanced wick effect

Nitrogen reflow oven is a very good choice for the following situation:

  • OSP surface treatment double side reflow welding plate is suitable for nitrogen.

②Parts or circuit board can be used when tin eating effect is not good

③After the use of nitrogen, it is necessary to pay attention to whether the bad tombstone is increased, and also check whether the soldering foot of connector is too high?

3. Process parameters affecting reflow soldering quality

How does the reflow oven work?

In general, there are four steps in the reflow oven process. The standard reflow profile has four zones: preheat zone, soak zone, reflow zone and cooling zone.

3.1 Working process of the reflow oven

① Preheat zone of the reflow oven

The purpose of this area is to heat the PCB at room temperature as soon as possible to achieve the second specific goal, but the heating rate should be controlled within a proper range.

If it is too fast, it will produce thermal shock, and the circuit board and components may be damaged;

If it is too slow, the solvent volatilization is not sufficient, which will affect the welding quality. Because of the fast heating speed, the temperature difference in the later SMA is large.

In order to prevent the damage of components caused by thermal shock, the maximum speed is generally specified as 4 ℃ / s. However, the rise rate is usually set at 1-3 ℃ / s. The usual heating rate is 2 ℃ / s.

② Soak zone of the reflow oven

Insulation section refers to the area where the temperature rises from 120 ℃ – 150 ℃ to the melting point of solder paste.

The main purpose is to stabilize the temperature of each component in SMA and reduce the temperature difference as much as possible.

Reflow oven heating zone 3D display – photo source

Give enough time in this area to make the temperature of larger components catch up with that of smaller components, and ensure that the flux in the solder paste is fully volatilized.

By the end of the insulation section, the oxide on the solder pad, solder ball and element pin is removed, and the temperature of the whole circuit board is balanced.

In the real production, the operator needs to notice that all components on SMA should have the same temperature at the end of this section,

Otherwise, when the board is entering into the re-flux section, there will appear various bad welding phenomena on the board due to the uneven temperature of each part.

③ Reflow zone of the reflow oven

In this zone, the temperature of the heater is set high, which makes the temperature of the component rise rapidly. In the reflow section, the temperature of the welding value varies with the solder paste used.

Generally, it is recommended to add 20-40 ℃ to the melting point of the solder paste. For 63Sn / 37Pb solder paste with a melting point of 183 ℃ and sn62 / pb36 / ag2 solder paste with a melting point of 179 ℃,

The value temperature is generally 210-230 ℃, and the reflow time should not be too long to prevent adverse effects on SMA. The ideal temperature curve is that the area covered by the “end zone” beyond the melting point of solder is small.

④ Cooling zone of the reflow oven

In this zone, the lead-free tin powder in the solder paste has melted and fully wets the connected surface.

Then, the operator should set an appropriate cooling temperature to make it cooled as fast as possible, which will help to obtain bright solder joints and have good shape and low contact angle.

Also, slow cooling will lead to more decomposition of the circuit board into the tin, resulting in dark rough solder joints.

In the case of the end, it can cause poor tin staining and weaken the bonding force of the solder joint. The cooling rate of the cooling section is generally 3-10 ℃ / s, and the cooling temperature is 75 ℃.

In addition, we would like to talk one important element in the reflow oven working course: the reflow oven profile.

So, what is the reflow oven profile?

Actually, it is the soldering temperature curve referring to the point on SMA/SMD changes with time when SMA/SMD passes through reflow oven.

Besides, the temperature curve provides an intuitive method to analyze the temperature change of a component in the whole reflow soldering process.

This is very useful for obtaining the best weldability, avoiding damage to components due to over-temperature, and ensuring the welding quality. The temperature curve is tested by the temperature tester, such as the smt-c20 oven temperature tester.

3.2 Defect parameter of the soldering process

The main influence factor of reflow soldering on SMC / SMD is the thermal shock during soldering. A reliable temperature rising process must be set during operation to reduce the thermal shock stress.

If the setting of the reflow soldering process and the control quality of each previous process fail to meet the specified requirements, it will lead to various undesirable phenomena such as SMC / SMD.

The defects in reflow welding can be roughly divided into two categories, please have a look:

①The defects are related to metallurgical phenomena, including cold welding, non-wetting, poor wetting, etc.;

②The defects are related to abnormal solder joint shape, including monument, bridge, core suction, solder ball, cavity, etc.

The main defects and the related reason & Elimination method are listed below:

Reflow oven soldering defects

⑴Displacement of components after reflow soldering

Reason: Defect Elimination method
Wrong location Calibrate positioning coordinate
Insufficient amount of solder paste or pressure for positioning Increase the amount of solder paste, increase the pressure of placing components
The flux content in the solder paste is too high, and the flux flow in the reflow process leads to component displacement Reduce the content of flux in solder paste

(2)After reflow soldering, solder paste welding powder can’t flow anymore, and it is scattered on the pad in powder form

Solder paste

Reason: Defect Elimination method
Improper heating temperature Improve heating equipment and adjust the temperature curve of reflow soldering
Solder paste deterioration Pay attention to the cold storage of the solder paste and discard the hardened or dry part of the solder paste surface
Excessive preheating, time or temperature Improve preheating conditions
  • The reflow solder joint is insufficient and less solder

Solder joint

Reason: Defect Elimination method
Insufficient solder paste Enlarge the aperture of wire mesh and leakage plate
Poor welding performance of pads and components Use solder paste or re impregnate components
Short reflow time Longer reflow time
  • Too much solder in reflow solder joint
Reason: Defect Elimination method
Too large screen or leakage plate aperture Reduce the diameter of wire mesh or leakage plate
Low viscosity of solder paste Increase paste viscosity
  • After reflow soldering, the components are firm, and the “Manhattan” phenomenon appears (“stele”)

Manhattan

Reason: Defect Elimination method
Displacement of placement position Adjust the parameters of solder paste printing machine
Flux in solder paste makes components float Use solder paste with less flux content
Insufficient thickness of printing solder paste Increase printing thickness
Heating speed is too fast and uneven Adjust reflow temperature curve
Unreasonable pad design Pad design in strict accordance with specifications
Using Sn63 / Pb37 solder paste Use paste containing Ag or Bi instead
Poor weldability of components Select solder paste with good weldability
  • Solder ball after reflow welding

Solder ball

Reason: Defect Elimination method
Heating too fast Adjust reflow temperature curve
Solder paste absorbs moisture Reduce ambient humidity
Solder paste is oxidized Use new solder paste to shorten preheating time
PCB pad contamination Change PCB or increase solder paste activity
Too much pressure on components Reduce pressure
Too much solder paste Reduce the hole diameter and pressure of scraper
  • Faulty reflow

Faulty reflow

Reason: Defect Elimination method
Poor solderability of pads and components Strengthen the screening of PCB and components
Incorrect printing parameters Reduce paste viscosity, check scraper pressure and speed
Improper reflow temperature and temperature speed Adjust reflow temperature curve
  • Continuous bridging after reflow
Reason: Defect Elimination method
Solder paste collapse Increase the metal content or viscosity of the solder paste, and change the solder paste
Too much solder paste Reduce the diameter of wire mesh or leakage plate, and reduce the pressure of scraper
Multiple printing on pad Using other printing methods
Heating too fast Adjust reflow temperature curve

Soldering bridge

  • Solder paste collapse
Reason: Defect Elimination method
Low viscosity and poor thixotropy of solder paste Choose the right solder paste
High ambient temperature Control ambient temperature
  • The reflow solder paste has poor washability, leaving white residue after cleaning
Reason: Defect Elimination method
Poor wash ability of flux in solder paste Solder paste prepared with a good washable flux
The cleaning agent does not match, and the cleaning solvent cannot penetrate into the pores Improve cleaning solvent
Incorrect cleaning method Improve cleaning methods

4. Reflow oven profile is the important tool to reflect quality

Why the the reflow oven profile can reflect the quality?

As to this question, you can find the answer in the following contents.

4.1 Definition of reflow oven profile

Reflow soldering is to achieve a good reflow soldering effect by adjusting the temperature curve of reflow soldering. The reflow soldering temperature curve intuitively reflects the process of temperature change of PCB welding in the reflow soldering furnace.

Reflow oven profile

If reflow soldering is not conducted according to the temperature curve of reflow soldering, it is easy to cause a large number of bad reflow soldering products.

From the temperature curve analysis, when PCB enters the temperature rise zone (dry zone), the solvent and gas in solder paste evaporates,

while the flux in solder paste moistens the pad, component end and pin, solder paste softens, collapses and covers the pad, and isolates the pad, component pin and oxygen gas;

When PCB enters the heat preservation area, the PCB and components will be fully preheated to prevent PCB from entering the welding area, and damaging PCB and components due to too fast temperature rise;

Then, when PCB enters the welding area, the temperature will rise rapidly to make solder paste melt, and liquid solder will wet, diffuse, diffuse or reflow the pad, component end and pin of PCB to form solder joint;

PCB enters into the cooling area to solidify the solder joint and complete the whole reflow welding.

4.2 How to get the reflow oven profile

Because of the structure and working principle of reflow soldering equipment, the set temperature of the temperature zone will be different when it is reflected on the products. The interval temperature displayed on the reflow soldering equipment is not the actual interval temperature.

The displayed temperature only represents the ambient temperature sensed by the thermistor couple in the temperature zone. If the thermocouple is close to the heating source, the displayed temperature will be higher than that of other areas in the temperature zone.

The closer the thermocouple is to the transmission track of the printed circuit board, the more the displayed temperature will reflect the actual temperature of the product.

Therefore, after setting the temperature, it is necessary to measure the product to get the actual temperature of the product, analyze the set temperature and modify it to get an optimal temperature curve for a product.

①Equipment and auxiliary tools needed for temperature curve measurement of reflow soldering furnace:

Temperature curve instrument: generally, there are two types of thermometer.

One is real-time thermometer, which can transmit temperature, time data and make graphs in real time.

Another is non real time thermometer, through sampling, storage, and then upload the collected data to the computer for analysis.

Thermocouple: medium used to sense the ambient temperature. Its working principle is that the circuit is composed of two different components of conductors.

When there is a temperature difference between the temperature measuring end and the reference end, the thermal current will be generated in the circuit, and the change of the external temperature will be reflected by the magnitude of the current.

Thermocouples with small diameter are generally required, because of their small thermal mass and fast response, the results are more accurate. Tools for attaching thermocouples to printed circuit boards: solder, adhesive, high temperature tape.

②Selection of test points for reflow soldering temperature curve:

In fact, in the process of producing a printed circuit board, the temperature of various components in each area of the board is not the same. Besides, the hot air in the furnace flows in the furnace under the action of the hot air blower

(flows from the upper and lower heating plates to the transmission track direction, and spreads along the surface of the printed circuit board to the edge of the board when encountering the barrier, so that the central area of the board becomes the place with the lowest temperature).

PCB testing points

The size of components also determines the temperature. Small components have high temperature and large components have low temperature.

Therefore, in the actual measurement, it is very important to reflect the real temperature of the tested products.

the following principles will help you with making a better temperature test:

  • Select as many points as possible when conditions permit.
  • The measured points shall be selected on the same longitudinal axis as much as possible.
  • Components with special requirements for temperature.
  • The position with the highest temperature of the board surface.

5) The lowest temperature of the board surface.

③Measure the temperature curve of reflow soldering and fix the thermocouple:

After selecting the tested point, the thermocouple shall be installed at the tested point.

Generally, there are several methods as follows:

  • The thermocouple is fixed by solder, and the high temperature solder with high Pb content is generally used to fix the thermocouple at the tested point.

It is required that the solder joints should be as small as possible, because the solderability of high-temperature solder is not high,

therefore, the operator should have the high welding skills, and the thermal impact on components is also large because of high-temperature welding. The effect of temperature measurement is better.

  • Use adhesive to fix, generally use epoxy resin adhesive to fix the thermocouple at the tested point. The glue point should be as small as possible. The effect of temperature measurement is general.
  • We should apply the High temperature tape to fix the thermocouple, what is more the tape should be with high temperature resistance and good thermal conductivity. Also, it needs to keep the thermocouple as close to the measured point as possible.

This method is easy to operate, but the effect of measurement is the worst. In each method, the measuring end of the thermocouple should be as close to the measured point as possible, so as to get a more real measurement result.

④Reflow soldering temperature curve measurement methods:

  • Analyze the thermal performance of PCB and select the tested point.
  • Attaching the thermocouple to the PCB below In order to ensure the accuracy of the measurement results, the printed circuit board to be tested shall be completely pasted.

Thermocouple tip

  • Trigger the thermometer to start recording the data and put the thermometer together with the tested printed circuit board into the reflow soldering furnace. We should notice two critical factors here:

The first point: there are two kinds of thermometer, one is to start recording data immediately after triggering, which requires that the thermometer be put into reflow soldering oven in the shortest time after triggering, so as to ensure the accuracy of the measured reflow time.

Another kind of thermometer is temperature sensitive type, when the ambient temperature rises to 40 ℃ (generally higher than the body temperature, it is used to ensure that no data will be recorded during the operation phase.)

Only when the data is recorded, there is no requirement for the insertion time of the thermometer.

Second point: in order to restore the actual environment of production to the maximum extent, the number of pass plates in normal production shall be ensured in front of the tested plates.

Once we have put the tested plate into the furnace chamber, then we can not put the product again to avoid accidents.

  • Finally, the temperature measuring instrument which collects data from the furnace is connected to the computer to generate the temperature curve.

⑤ Analysis of reflow soldering temperature curve and furnace temperature adjustment:

Before analyzing the reflow temperature curve, it is necessary to master the data of several control points:

1) Determine the total time from ambient temperature to peak reflux temperature.

2) Process parameters (temperature, time, heating speed) of each temperature zone.

The specific adjustment method of reflow soldering temperature curve is as follows:

Firstly, the total time from ambient temperature to reflow peak temperature is matched with the desired residence time of heating curve by adjusting the conveyor belt speed.

Next, the deviation of the curve (flow sequence) should be adjusted from left to right to ensure that the shape of the overall curve is consistent with the process parameters and given standards of each temperature zone.

For example: if there is a difference between the preheating area and the re-flux area, the difference in the preheating area shall be adjusted correctly first, and it is better to adjust one parameter at a time.

Before further adjustment, the adjusted curve shall be run first and the new curve shall be measured before adjustment.

Because the temperature change of a given temperature zone will affect its subsequent temperature change. Thus, we should adjust the furnace temperature curve step by step.

4.3 Key elements to affect the temperature of reflow oven

①Transfer of hot air in reflow soldering

In lead-free welding, we should pay to heat transfer effect and heat exchange efficiency.

Especially for the components with large heat capacity, if they can’t get enough heat transfer and exchange, the heating rate will obviously lag behind that of the components with small heat capacity, then resulting in the transverse temperature difference.

Reflow oven hot air transfer

The design of the air transport structure of the reflow soldering furnace directly affects the heat exchange rate. There are two ways of hot air transfer in reflow soldering. One is microcirculation hot air transmission mode, the other is small circulation hot air.

②Heat transfer mode of reflow soldering

The hot air in the microcirculation hot air blows out from the holes of the heating plate. The flow of the hot air flows in a small range, and the surrounding heat transfer effect is not good. The design of small circulation is due to the flow concentration of hot air and clear direction.

The heat transfer effect of this kind of hot air heating increases about 15%, and the increase of heat transfer effect will play a greater role in reducing the transverse temperature difference of large and small heat capacity devices.

③Control of chain speed of reflow soldering

The control of chain speed will affect the transverse temperature difference of circuit board. Generally speaking, reducing the chain speed will give more heating time to devices with large heat capacity, thus reducing the transverse temperature difference.

The chain of reflow oven

But after all, the setting of furnace temperature curve depends on the requirements of solder paste, so it is unrealistic to reduce the chain speed in actual production.

④Control of air speed and air volume in reflow soldering

In order to control the wind speed and air volume, we should keep the following two points in mind:

  1. In order to reduce the influence of voltage fluctuation, we should apply the frequency conversion to control the speed of fan;
  1. Try to reduce the exhaust air volume of the equipment, because the central load of the exhaust air is often unstable, which is easy to affect the flow of hot air in the furnace.
  1. Equipment stability

Even if we get the best setting of furnace temperature curve, we still need to use the stability of the equipment to realize it.

In the reflow welding production process, if the furnace temperature curve slightly drifts due to equipment reasons, it is easy to jump out of the process window and causes the cold welding or original device damage.

Now more and more manufacturers begin to put forward the requirements of stability test for equipment, and the quality of reflow welding temperature control affects the quality of reflow welding quality directly.

5. How to set the parameter to get the good reflow oven profile?

5.1 Setting of the Chain

The first parameter we should consider when setting reflow soldering temperature curve is the speed setting of transmission belt, which will determine the time spent by PCB passing through heating channel.

Through the specific calculation, we can get the setting of belt speed. Here we need to introduce an indicator, load factor. Load factor: F = L / (L + s) l = length of base plate, s = interval between base plate and base plate.

Transmission belt and chain

The load factor determines the influence of PCB in the furnace on the temperature in the furnace. The larger the load factor is, the more unstable the temperature in the furnace is. Generally, the value is between 0.5 and 0.9.

After weighing the efficiency and the stability of furnace temperature, the recommended value is 0.7-0.8. After knowing the length of the production board and the production beat, then we are able to calculate the transmission speed (the slowest value) of the conveyor belt.

Transmission speed (slowest value) = PCB length / 0.8/production beat. The characteristics of solder paste decides the transfer speed (the fastest value).

Most solder paste requires that the time from the beginning of temperature rise to the peak temperature in the furnace should not be less than 180 seconds.

By this way, the transfer speed (max.) = the length of the heating zone in the furnace / 180s can be obtained.

After obtaining two limit speeds, we can select the appropriate transmission speed according to the difficulty degree of the actual production products, generally taking the intermediate value.

5.2 Temperature of the reflow oven

① According to the specific conditions of the equipment, such as the length of the heating area, the material of the heating source, the structure of the reflow soldering furnace and the heat conduction mode, etc.

Reflow oven temperature setting

②Set in keep with the temperature curve of the solder paste used. Solder paste with different metal content has different temperature curve. The reflow temperature curve of specific product shall be set according to the temperature curve provided by solder paste supplier.

③Set according to the size of exhaust air volume. General reflow soldering furnace has specific requirements for exhaust air volume, but the actual exhaust air volume sometimes changes due to various reasons.

When determining the temperature curve of a product, the exhaust air volume shall be considered and measured regularly.

④The setting temperature of each temperature zone is determined according to the actual position of the temperature sensor. If the temperature sensor is located inside the heating body, the setting temperature is about 30 ℃ higher than the actual temperature.

⑤ Set according to the material, thickness, multi-layer board and size of PCB.

⑥It is set according to the density and size of components on the surface assembly board as well as special components such as BGA and CSP.

With the increase of assembly density of electronic products and the decrease of component size and pin spacing, the difficulty of SMA welding process is increased, the setting range of reflow welding temperature curve parameters is narrowed, and welding quality problems are easy to occur. The correct design of welding process, especially the accurate setting of welding temperature curve, has become one of the key contents to ensure the quality of SMA assembly.

6. Operation and maintenance of the reflow oven

6.1 Operation of the reflow soldering oven

Reflow oven operator

①Shut down and cut off the power supply when repairing the machine to prevent electric shock or short circuit.

②The operator should carry out daily inspection of all parts for reflow welding, and pay special attention to the conveyor belt to prevent it from jamming or falling off.

③The temperature measuring equipment can not be in the high temperature state for a long time. After each temperature measurement, the temperature measuring equipment shall be quickly pulled out from the furnace cavity to avoid deformation.

In case of stopping heating in individual temperature areas, the corresponding safety pipe shall be checked first. During operation, attention shall be paid to avoid scalding at high temperature.

During the cooling mode, the operator should open the furnace to check whether there is any foreign matter in the furnace cavity, the close the furnace body at the end.

④Start reflow soldering and check whether the sound of hot air motor is abnormal.

Check whether the conveyor belt is normally squeezed and jammed during transportation. Ensure that the chain and each sprocket are well engaged and derailed.

Check the lubrication of each roller bearing. If any abnormality is found, press the emergency stop button immediately to prevent damage to the equipment.

⑤Operators shall regularly check and maintain reflow soldering equipment and make records.

⑥Check the power supply to check whether the equipment is well grounded, and check the reflow oven cavity to ensure that the internal foreign matters of the equipment.

⑦ Open the control software to set the temperature of reflow soldering. Generally, the furnace temperature reaches the set value in 20-30 minutes.

⑧The computer on the device is for the machine using. It is strictly prohibited to delete or change the data files, system files and batch processing files configured by the computer at will to avoid computer system confusion.

Notice: Do not use any mobile storage device to communicate with the computer without permission.

⑨Adjust the width of the guide rail slowly according to the size of the circuit board. The machine must be stable without tilting or instability. During operation, it is strictly prohibited to put other items into the furnace cavity except the circuit board and temperature measuring equipment.

⑩ Check that the four emergency switches at the end of the entrance and exit spring up and remove the four emergency switch protection rings.

⑪Check the power supply error of exhaust fan and then connect the power supply.

⑫Do not cut off the power supply before reflow soldering shutdown. The system will automatically enter the cooling operation mode. The hot air motor will continue to work for 10-15 minutes, and then the hot air motor will stop working. Then the heat source can be turned off.

6.2 Maintenance of the reflow soldering oven

Reflow oven maintenance

In order to prolong the service life of reflow soldering, ensure the stable production of SMT, improve the output and ensure the product quality, every part of reflow soldering needs to be maintained very carefully.

①Track parallelism:

Measure the distance with vernier caliper. Adjustment method: take the width of the inlet as the reference point.

If the outlet is wide or narrow, using the fixed pliers and 19mm open-ended wrench to separate and loosen the chain and the rear end rotating gear bar of the track, and then turning the front and rear end transmission gear bar by hand to adjust to the same distance as the front and middle end.

②Track moving device:

If the track moving device fails to slide smoothly, it is necessary to manually adjust the track width to the limit and walk back and forth in the temperature range, and observe whether the track width is affected by the main force. If it is too tight, loosen the mobile device.

③Front and rear iron and steel plates of the fixed side of the track:

In addition to checking whether the iron and steel plates are offset with a level gauge, it is also necessary to check whether the fixing screws of the track are loose with a hexagon wrench. Ensure that the position of steel plate before and after the fixed edge of the track is stable and correct.

④Gear chains of track width adjustment drive motor:

It is necessary to check whether the gears and chains rotate normally, and the fixing screws of the axle center cannot be loosened, and keep their surfaces clean at all times, and then lubricate the gears and chains with lubricating oil.

⑤To adjust the width of the transmission rod:

The transmission rod needs to rotate normally, without dirt, deviation, bending or deformation. The rod surface must be kept clean and lubricated.

⑥Front end and middle fixed gear bar and gear:

They must be engaged normally, and there shall be no dirt, deviation, bending and other deformation.

⑦Middle fixed gear bar assembly:

It must move synchronously with the transmission motor, and travel smoothly. Remember to use a hex wrench to tighten the screws before checking the engagement.

7. Advantage and disadvantage of the DIY reflow oven

7.1 How to make a DIY reflow oven?

DIY reflow oven

Hobbyists and educational institutions obviously cannot afford to purchase the mammoth part placement machines or reflow ovens which can be used presently in the industry.

Consequently, makeshift ovens have popped up everywhere in the region that are using a quite a lot of substitutes along with toasters, skillets, and ovens.

Due the truth that those ovens are a diversion from industry, there may be no constant standard as the way to move approximately. All this is technically required so far for a reflow to arise is to exceed a temperature of approximately 200C.

At 200C in temperature, maximum sorts of solder will start to flow. While those equipment can be capable of flowing solder, their protection and reliability are placed into question.

Hence, the performance and reliability of the oven are absolutely as much as the builder and the functions that they determine to implement.

For example, a number of DIY reflow ovens will put into effect enhance sensors together with a couple of thermocouples for warmth control, stable state relays for electricity control, and convection fans for even heat distribution.

The features that are implemented generally depend on the budget and emphasis of the designer on component safety.

In regards to safety, additives are rated primarily based totally upon intervals of excessive temperature publicity and going above those ranges can lead to component destruction.

As an end result of this, enterprise reflow ovens observe a strict reflow oven profile. Likewise, a DIY oven is also graded based upon how closely it can follow a given profile.

8. How to choose a good reflow oven manufacturer?

8.1 How to choose a good reflow oven?

Selection

  1. The temperature control accuracy shall reach 1 ℃ (theoretical value):

The influence of temperature control accuracy and the way of reflow soldering heat generator is related to the way of heating and heat transfer.

a: Heating wire type heating element (usually made of imported Ni Cr wire), which has high exchange rate and long service life;

b: Infrared tube heater (imported far-infrared heating tube is used). This kind of heater is radiation type, with good uniformity, but it will produce color temperature difference. It is mainly used in heat compensation area and not suitable for welding area.

c: Heating tube type heating body, which has low heating efficiency. If it does not pass hot air, the uniformity of heating surface is not good (generally less used);

Heating and heat transfer mode: full hot air circulation (good) and hot air circulation + infrared composite (good) and full red external (bad).

  1. The transverse temperature difference of the conveyor belt shall be below 5 ℃, otherwise it is difficult to ensure the welding quality. High quality reflow welding can be controlled at 2 ℃ / 3 ℃ (pE6 and pe8 Series).
  1. The width of conveyor belt shall meet the requirements of maximum PCB size. According to your PCB, choose the mesh belt width: PCB 200mm, choose the mesh belt application of 300mm,

In general: 300 350 400 450 500mm, the larger the selection width is, the greater the reflow welding power will be, so the most important thing is to choose the right one

  1. The longer the heating zone is and the more heating zones are, the easier to adjust and control the temperature curve.

Generally, 5-6 temperature zones are selected for medium and small batch production, and the reflux furnace with a heating zone length of about 1.8m can meet the requirements.

In addition, the upper and lower heaters shall be controlled independently to adjust and control the temperature curve.

As to standard lead-free production, we usually have 8 temperature zones, according to different production requirements.

Control system: computer system cooperates with Siemens system to select computer type reflow soldering to test whether the computer crashes or is removed, which will affect production.

If the system board of industrial computer is not good in cartoon use and does not have storage function, once the computer system has problems, the equipment can not be used Class a system has low cost, so it is not recommended to purchase such models.

  1. The maximum heating temperature is generally 300 ~ 350 ℃. If lead-free solder or metal substrate is considered, 350 ℃ or above should be selected.

Different reflow soldering has different heat preservation performance. Generally, the low-grade products do not have enough heat preservation layer, and the maximum temperature is usually less than 300 ℃.

Generally, the reflow soldering design that the design temperature can reach 300 ℃ or above is more than 320-350. If the reflow soldering of radiator is more than 400 ℃

  1. The conveyor should be able to run stably, because the vibration of the conveyor belt will cause the displacement, suspension bridge, cold welding and other welding defects.

For the reflow welding of middle and low gear, the transmission mechanism is relatively simple, and there will be a little vibration.

Reflow oven conveyor mesh

  1. For a good reflow soldering, the control circuit should have the anti-interference circuit design. The inverter and external impulse voltage will affect the stability of reflow soldering. If no relevant treatment is done, the manufacturer is not recommended to purchase the equipment.
  1. It shall have the function of temperature curve test. If the equipment does not have this configuration, the temperature curve collector shall be purchased.

From the above analysis, we can see that PCB design and processing quality, components and solder paste quality are the basis to ensure the quality of reflow soldering, because these problems are difficult or even impossible to solve in the production process.

At the same time, it can be seen that as long as the PCB design is correct, the quality of PCB, components and solder paste is qualified, and the reflow welding quality can be controlled by the process of printing, mounting and reflow welding.

In short: choose a good reflow soldering, do not only pay attention to its appearance, good equipment is usually imitated in the market, performance and energy saving, safety considerations in many ways.

8.2 How to choose a good reflow oven manufacturer?

Reflow oven supplier

Detail checkpoints for choosing the reflow oven manufacturer, please check the following:

  1. Check out the years of experience they have.

Those who have been in business for a couple of years are the ones who have served a wide range of clients.

In this situation, you are guaranteed that the company you choose is reputable in the industry. Selecting them is better since there is a great chance that they provide nothing but the best products you are searching for.

  1. Next, check their licenses.

Basically, all businesses are mandated to have a license for them to properly and legally operate. The licenses and permits can only be obtained once they are able to submit all required documents to prove that they are truly and legal and reliable company.

Also, it gives an assurance for all customers that they are dealing with the right business.

Aside from that, you have to check the warranties they are giving. When buying a machine from a specific manufacturer,

make sure to check first this factor as it offers you a guarantee that in the event there are issues such as damages on the machine, you can return it easily to the company for a replacement or repair for free.

  1. The cost is another consideration to make.

People opt to buy the cheapest ones to save more costs without knowing the effects. While you can save for buying cheap products, you can never assure the overall quality of the product and may only require you to spend more money later on.

9. How to choose a reflow oven?

9.1 Is the price the main factor?

Reflow oven price

How to select reflow soldering equipment can not only meet reflow specification of solder paste manufacturer, but also provide reliable and high-quality welding performance.

When purchasing reflow welding equipment, many manufacturers don’t know how to choose it.

Hence, we list some suggestions here for your reference:

①Maximum number of return plates

Assuming that at maximum capacity you have to load the plate end-to-end on the conveyor of the reflow equipment, it is easy to calculate the maximum production.

For example, in case your board has a 7 inches length and the band speed ability of a 6-zone reflow soldering oven is 17.9-20.2 inches every minute, the most throughput of that reflow soldering is 2.6 to 2.9 boards every minute. That is to say, about 20 seconds up and down the circuit board will be welded.

②Heating time of solder paste

The temperature of reflow soldering equipment should follow the requirements of solder paste.

Solder paste manufacturers usually provide quite wide window time for each stage of reflow curve: preheat and constant temperature time 120 to 240 seconds, reflow time 60 to 120 seconds / liquid above.

We discovered that a median overall heating time of four to four 1 / 2 minutes (240-270 seconds) is a good, surprisingly conservative estimate.

For this simple calculation, we suggest that you ignore the cooling link of welded profiles. Cooling is important, but generally does not affect the welding quality unless the PCB cools too fast.

③Length and number of heating zones

The longer the heating zone is, the more heating zones there are, the easier it is to adjust and control the temperature curve.

Generally, 5-6 temperature zones are better for medium and small batch production, and the reflux furnace with a heating zone length of about 1.8m can meet the requirements.

In addition, the upper and lower heaters shall be controlled independently to adjust and control the temperature curve.

④ The width of the conveyor belt shall meet the requirements of maximum PCB size

According to your PCB selection mesh belt width: PCB 200mm mesh belt application selection 300mm,

In general: 300 350 400 450 500mm 600mm the larger the selection width is, the greater the reflow welding power will be, so the most important thing is to choose the right one.

⑤ What other factors affect reflow soldering equipment

In addition to the above factors, there are many other factors to consider.

For example, a double-sided board and manual assembly operation will affect the efficiency of reflow soldering.

According to the actual situation of our factory and the output of other processes, we should choose the appropriate reflow welding equipment.

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