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Wave solder welding in SMT assembly process

Wave solder welding in SMT assembly process

Wave solder ; welding
Wave solder welding in SMT assembly process

The SMT assembly process is closely related to each process before welding, including capital input, PCB design, component weldability, assembly operation, flux selection, temperature / time control, solder and crystal structure, etc.

At present, the most commonly used solder for wave soldering is eutectic tin lead alloy: tin 63% and lead 37%. The temperature of solder in the soldering pot should be mastered at all times. The temperature should be higher than the temperature of the alloy at 183 C, and the temperature is uniform. In the past, the temperature of soldering pot at 250 degrees was regarded as “standard“.

With the innovation of flux technology, the uniformity of the solder temperature in the whole solder pot is controlled and the preheater is added. The development trend is to use the solder pot with low temperature. It is common to set solder pot temperature at 230-240 degrees Celsius. Usually, the components do not have uniform thermal quality. It is necessary to ensure that all solder joints reach enough temperature to form qualified solder joints. The important problem is to provide enough heat to raise the temperature of all leads and pads, thus ensuring fluidity of solder and wetting both sides of solder joints. The low temperature of the solder will reduce the thermal shock to the component and the substrate, and help to reduce the formation of the slag. Under the lower strength, the flux coating operation and the flux compound can make the peak of the wave with sufficient flux, thus reducing the burr and welding ball. The solder composition in the solder pot is closely related to the time, which changes with time, which leads to the formation of the scum, which is the reason for the removal of residual and other metal impurities from the welded components and the loss of tin in the welding process.

These factors can reduce the fluidity of the solder. The maximum limit of tin content in metal scum and solder should be specified in the procurement. In the welding process, the requirements for the purity of solder are also specified in the ANSI/J-STD-001B standard. In addition to the limitation of scum, the minimum content of tin in 63% tin and 37% lead alloys should be no less than 61.5%. The concentration of gold and organic swimming layer on the wave soldering assembly is faster than in the past. This aggregation, combined with obvious tin loss, can cause solder loss of fluidity and produce welding problems. Rough and granular solder joints are often caused by scum in solder. Because of the concentrated pomum in the solder pot or the innate and coarse grainy welding spot of the component itself, it may also be a sign of low tin content, not a local special solder, or the result of tin loss in the tin pot. This appearance may also be caused by vibration or shock during solidification.

The appearance of solder joints can directly reflect technological problems or material problems. In order to maintain the “full pot” state of the solder and to analyze the solder pot according to the process control plan, it is very important to analyze the solder pot. The flux in the soldering pan is usually not necessary because of the dross in the soldering pan, which is usually unnecessary, because the solder in the tin pot is required in the conventional application to make the solder in the tin pan always full. In the case of loss of tin, the addition of pure tin helps to maintain the desired concentration. In order to monitor the compounds in tin pot, routine analysis should be carried out. If tin is added, sampling and analysis should be taken to ensure the correct proportions of solder components. Too much scum is a tricky problem. There is no doubt that there are always scum in the tin pot, especially when welding in the atmosphere. The use of “chip wave peak” is very helpful for high density welded components. Because the surface of the material exposed to the atmosphere is too large to oxidize the solder, more dross will be produced. The solder is covered with a scum layer and the oxidation rate slows down. In welding, more turbulence will occur due to the turbulence and flow of the crest in the tin pot. The recommended method is to skim the scum. If skipping regularly, more scum will be generated and more solder will be consumed. Scum may also be involved in the wave crest, causing the instability or turbulence of the crest. Therefore, it is necessary to give more maintenance to the liquid components in the tin pot. If the amount of solder in the tin pot is allowed to reduce, the scum on the solder will enter the pump, which is likely to happen. Sometimes, granular solder joints are mixed with scum. The scum found initially may be caused by rough crest and may block the pump. Tin pots shall be equipped with adjustable low capacity solder sensors and alarm devices.

Wave solder;welding
Wave solder welding in SMT assembly process

Crest is the core of wave crest in wave soldering process. The most critical step is to bring the preheated, coated, and non – dirt metal through the conveyor belt to the welding workstation, contact the solder with a certain temperature, and then heat it, so that the flux will produce chemical reactions, and the solder alloy forms interconnect through the wave peak power. At present, the commonly used symmetrical peak is called the main wave peak, which sets the pump speed, wave peak height, depth of infiltration, transmission angle and transmission speed, so as to provide a full range of conditions to achieve good welding characteristics. The data should be adjusted properly, and the solder should be slowed down and slowly stopped after leaving the crest. PCB with the wave crest running, the solder will be pushed to the outlet. In the most reliable case, the surface tension of solder and the optimal crest operation of the plate can achieve zero relative motion between the components and the crest of the outlet. This shelling area is achieved by removing solder from the plate. Sufficient inclination angle should be provided to avoid defects such as bridge, burr, wire drawing and solder ball. Sometimes, the outlet of the crest needs hot air flow to ensure that possible bridging is eliminated. When the surface mount element is installed at the bottom of the plate, sometimes, the bubbles in the “harsh wave peak” region formed in the back of the flux, and the wave peak is used before the wave peak is leveled. The high vertical velocity of the turbulent crest helps to ensure the contact between the solder and the lead or pad. The vibration part behind the leveling laminar peak can also be used to eliminate bubbles and ensure satisfactory contact components of the solder. The welding workstation should basically achieve: high purity solder (according to standard), wave peak temperature (230~250 degrees C), total time of contact peak (3~5 seconds), depth (50 ~ 80%) of PCB immersed in wave peak (50 ~ 80%), to achieve parallel transmission track and flux content in tin pot in parallel state of wave peak and orbit. Cooling after wave soldering is usually equipped with cooling workstations at the end of the wave soldering machine. It is a trend to restrict the formation of solder joints between copper and tin intermetallic compounds, and the other is to accelerate the cooling of the components, and to avoid the plate displacement when the solder is not fully solidified. The rapid cooling assembly is designed to limit the exposure of sensitive components to high temperatures. However, the danger of corrosive cooling system to thermal shock of components and solder joints should be taken into account. A well controlled “soft, stable” and forced gas cooling system should not damage most components. There are two reasons for using this system: it can process the board quickly without hand holding, and ensures that the temperature of the component is lower than that of the cleaning solution. People are concerned about the latter reason, which may be responsible for the foaming of some flux residues. Another phenomenon is that sometimes there is a reaction with some flux dross, so that residues can not be washed away. No formula can meet the requirements of all machines, all designs, all materials and technical material conditions and requirements that are guaranteed to meet the data set by the welding workstation. We must understand every step of the whole process. 4 conclusion in conclusion, in order to obtain the best welding quality and meet the needs of the users, every step in the pre welding and welding process must be controlled, because each step of the assembly process of SMT is interrelated and interacted with each other, and any step has the dependability and quality in the whole. Welding operation is also the case, so all parameters, time / temperature, solder volume, flux composition and transmission speed should be strictly controlled. For the defects produced in the welding, the causes should be identified early, and the corresponding measures should be taken to eliminate all the defects that affect the quality in the bud. In this way, the products produced can be guaranteed.

 

How to prevent static electricity in the process of SMT placement machine?

How to prevent static electricity in the process of SMT placement machine?

Southern Machinery Anti Static Tools & Supplies
Southern Machinery Anti Static Tools & Supplies

In the SMT production line, we will encounter the problem of static electricity, from the friction between the clothes and the dry air to the dry air, which is the end of the duckweed. If the condition is suitable, it is a few volts and the peak is hundreds of kilovolts, so anti static is the need to do in our work, today, the south. Give some measures to introduce mechanical anti electrostatic patch SMT.

static clothing, antistatic shoes (conductive shoes)
static clothing, antistatic shoes (conductive hats)

Http://www.smthelp.com

Static electricity has three: static clothing, antistatic shoes (conductive shoes), electrostatic hand rings, antistatic shoes and electrostatic hand rings to guide the human body to avoid accumulation in the human body.
Ordinary clothes will have great electrostatic voltage in the walk (>1000V). And antistatic clothing does not happen when it moves. This is the main role of antistatic clothing, long strip antistatic clothing can not shield the inside of the clothing produced static (after wearing still >1000V), grid – like antistatic clothing can be shielded (<200V), the static electricity generated through the floor and the grounding line of various parts of the plant to the outside of the general grounding wire.

Http://www.smthelp.com

一,The purpose of preventing static electricity

1, strengthen the consciousness of the workers on the anti static operation

2, reduce the poor production caused by static electricity

3, prevent static electricity from causing damage to the product

二,Scope of application: all SMT production lines

三,The reasons

The generation of static electricity is not perceived, but the static electricity produces the voltage of tens of thousands of volts. When the static electricity comes into the tip (the static release point, such as the human finger), it releases all the energy in a moment, causing the contact material to be struck by electric shock, causing the capacitance, IC, line road and so on to be destroyed and burned, so that the product is strict. In the case of heavy damage, static electricity measures should be taken. .

四,The contents of the operation

Anti Static Tools & Supplies SMT magazine rack&turnover rack
Anti Static Tools & Supplies
SMT magazine rack&turnover rack

(一)Prevention and treatment of human static electricity

1, the workers should wear electrostatic clothing, work shoes;

2, the operator should take electrostatic gloves when working.

3, the operator should take an electrostatic ring in the operation.

(二)Prevention and control of static electricity

  1. Make use of electrostatic materials to produce production tools.

2, the storage place to prevent static electricity;

(三)Prevention and control of static electricity of a worktable / mobile vehicle

1, the anti static film should be pasted on the work table.

2, the operation platform / mobile vehicle must have antistatic grounding chain.Prevention of equipment static electricity: good grounding wire

(四)Prevention and control of material static electricity

  1. When the material is taken, the operator should use the antistatic method: with electrostatic gloves and electrostatic rings.

2, the material storage should be anti static measures: material cabinet to paste electrostatic film, grounding chain.

3, there should be anti-static measures in temporary storage area: installing grounding chain.

(五)Prevention and control of static electricity related to production: anti static measures should be taken when using items related to production: static wires and antistatic films.

 

五, Note:

  1. The online operators should strictly abide by this rule
  2. The online operators are supervised by the team leader, and the engineers are supervised by the engineers.

 

S-UV-300 laser marking machine for PCB

Product overview and industry application of laser marking machine

Abstract: The laser marking machine is means it use of  laser.  laser has the advantages of small volume (without water cooling, air cooling), good beam quality (fundamental mode), free maintenance etc, is mainly composed of laser, vibration lens, marking card three parts.

Guide: all you want to know about  laser machine knowledge is here!

S-UV-300 laser marking machine for PCB
S-UV-300 laser marking machine for PCB

In recent years, laser marking has become a hot topic in the study of laser physics. It is considered to be a new generation of products that may replace manual marking in an all-round way. The laser marking machine is a permanent mark on the surface of a variety of materials using a laser beam. The principle of marking is to expose deep matter through the evaporation of surface matter, or to engrave traces through the physical change of surface material caused by light energy, or to burn out some substances by optical energy to etch all kinds of graphics、patterns、characters、barcodes etc,.

The laser marking machine is means it use of laser. It has the advantages of small volume (without water cooling, air cooling), good beam quality (fundamental mode), free maintenance etc, is mainly composed of laser, vibration lens, marking card three parts.
Laser marking machine and its laser beam quality was good and with 1064 nm output center,it’s whole life is about 100 thousand hours,Laser compared with other types of markers for longer life. The efficiency of electro-optic conversion is above 28%, and the conversion efficiency of 2%-10% have a great advantage for other type of marking machine. It has excellent performance in energy saving and environmental protection.

Equipment features
1. A variety of metal and nonmetal materials can be processed. Especially for high hardness, high melting point and brittle material, it is more advantageous to mark the brittle material.
2. It belongs to non – contact processing, no damage to products, no tool wear and good marking quality.
3, the laser beam is fine, the processing material consumption is very small, and the processing heat affected zone is small.
4. The processing efficiency is high, the computer is controlled, and the automation is easy to be realized.

Application fields
Markers are widely used in many fields of graphics and text of integrated circuit chip, computer accessories, industrial bearings, watches, electronic and telecommunication products, aerospace devices, auto parts, household appliances, hardware tools, moulds, food packaging, jewelry, tobacco and military things, and mass production line.

Main features
Laser is divided into three kinds of types: CO2 laser/Green laser/UV laser. The following is a detailed introduction.
1, CO2 laser:10~20W, (laser wave is about 1064nm)
2, Green laser:7~10W(laser wave is about 532nm)
3,UV laser:3~5W(laser wave is about 355nm)
Laser marking machine is the most advanced marking equipment in the world. It has many advantages, such as good beam quality, small volume, fast speed, long service life, flexible and convenient installation, and low maintenance.Laser is the latest international, the most reliable structure, small volume, low power consumption.close to the ideal beam, the USB interface output control, optical scanner, laser with high repetition rate, high speed without distortion.

Future advantage
(1) low cost of manufacturing, mature technology and the availability.
(2) the light source has a very small volume area ratio, fast heat dissipation and low loss, so the up conversion efficiency is high and the laser threshold is low.
(3) the output of laser wavelengths is more.
(4)tunability: because of the wide fluorescence spectrum.
(5) the laser easy to apply to various multi-dimensional and arbitrary space processing applications, making the design of the mechanical system very simple.
(6) no thermoelectric refrigeration and water cooling are needed, only a simple air cooling is needed.
(7) high electro-optic efficiency: the integrated electro-optical efficiency is as high as 20%, saving the power consumption of the work and saving the operation cost.

S-UV-30A laser marking machine
S-UV-30A laser marking machine

IN application field to study the characteristics of fiber laser marking machine

IN application field to study the characteristics of fiber laser marking machine

The laser are use laser to make a chemical reaction on the surface of an object and leave a trace to form a label.Follow Southern Machinery to learn the main features of the fiber laser marking machine in detail.

1, long life and low maintenance:

Another feature of fiber laser marking machine is that its technology greatly extends the life of its devices, and makes the fiber laser marking function take longer time to improve its performance price ratio, which has become a hot topic of business. The structure of the cast aluminum and the solid fiber protection layer have raised its own strength, and the features of its small and sturdiness are fully displayed.

 

laser marking machine sample1
laser marking machine sample 1

2, small and sturdy:

The marking of fiber laser marking machine is small, and the use of air-cooled device without traditional water cooling device is one of the cause for its small size. The shortening and improvement of fiber length not only improve its quality, but also make its appearance smaller and more exquisite. It has been widely used in various fields and achieved good results. With the improvement of technology, the optical fiber laser marking machine has a very broad application prospect.

S-UV-30A laser marking machine for PCB
S-UV-30A laser marking machine

3.high performance and high stability.

The laser makes it permanently marked on the surface of a different material. Its power is powerful and the speed can reach 2.5m/s. The marking has high contrast, the laser beam is fine, the marking is more meticulous, and the quality of the marking is improved. And the non-contact processing improves the shortcomings of the wear tool, and does not damage the contact surface of the product, and can effectively reduce the consumption of the material. Laser processing is not polluted.  When using, we should pay attention to check whether the concentrator is polluted or not, and cut off the power without working. Regular cleaning can effectively maintain its performance and brand new low maintenance characteristics.

S-UV-300 laser marking machine for PCB
S-UV-300 laser marking machine for PCB

Conclusion:

due to fiber laser marking machine has the characteristics of small size, firmness, high performance, high stability, long life and low maintenance, it has rapidly become the research hotspot of laser physics, and has the potential to replace traditional laser marking machine.

 

DIP, PCB Assembly,Chip Mounter, Pick and Place, IC Mounter, High Speed Mounter, Wave soldering,LED lighting, LED Lamp, LED Display, LED tube,UPS, Power Converter, Power Adepter, Mobile Charger, PCB board handling system, Loader, Unloader, Conveyor,Shuttle, Chip Mounter, Pick and Place, IC Mounter, High Speed Mounter Induction Cooker, AC, Electric Cooker, Fan, TV, Settle Box

Reflow oven technology and precautions

Reflow oven technology and precautions

Far infrared reflow again

In 80s the use of far infrared reflow has the characteristics of fast heating, energy saving, stable operation, but because the printed circuit board and various components for different material, color and thermal radiation absorption rate to have very big difference, caused by a variety of different components and different parts of the circuit temperature is not uniform, the local temperature difference. For example, the black plastic package of integrated circuit will be overheated due to the high radiant absorption rate, and the welding part of it will lead to false welding on the silver lead instead of low temperature. In addition, the heat radiation blocked on printed boards, such as welding pins or small components in the shadow parts of big (high) components, will cause poor welding due to insufficient heating.

1.2 full hot air reflow again

Full hot air reflow oven  is a welding method by which the flow of airflow is forced through a convective nozzle or a heat-resistant fan, so that the welded parts are heated. This kind of equipment began to rise in 90s. Due to the adoption of this heating mode, the temperature of PCB and components is close to the temperature of the given heating area, which completely overcomes the temperature difference and shadowing effect of infrared reflow soldering, so it is widely applied now. In all hot air reflow oven  equipment, the convection velocity of the circulating gas is very important. In order to ensure that the circulating gas acts on any area of the printed board, the air flow must have a fast enough speed. To a certain extent, it is easy to cause the jitter of the printed board and the displacement of the components. In addition, in terms of heat exchange, the efficiency is poor and the power consumption is more.

1.3 infrared hot air reflow again

This kind of reflow oven is a more ideal heating method, which is based on the IR oven with hot air to make the temperature even more uniform insaide the oven. The characteristics of this kind of equipment to make full use of the infrared penetration, high thermal efficiency, energy saving, and effectively overcome the temperature difference of infrared reflow soldering and shadowing effect, and make up the influence of hot air reflow on gas flow caused by excessive demand, therefore  at international this kind of IR+Hot reflow is used most commonly  at present .

With the increase of assembly density and the appearance of fine spacing assembly technology, a reflow oven  furnace with nitrogen protection has appeared. Welding under nitrogen protection conditions can prevent oxidation, improve welding wetting power and speed up wetting speed. It is more suitable for uncleaning process to reduce the welding force and reduce welding beads.

2  The establishment of  temperature curve

The temperature curve is the curve of the temperature of a point on the SMA will change over time when SMA through the reflow oven. The temperature curve provides an intuitive method to analyze the temperature change of a component during the whole reflow process. This is very useful for obtaining the best weldability, avoiding damage to the components due to overheating, and ensuring the quality of the welding.

The following is a brief analysis of the preheating section.

2.1 preheating section

The purpose of this section is to put PCB at room temperature as soon as possible heating, to achieve second specific targets, but the heating rate should be controlled in the appropriate range, if excessive, will produce thermal shock, circuit boards and components may be damaged; if too slow, will not fully solvent, affecting the welding quality. Due to the rapid heating rate, the temperature difference in the rear section of the temperature zone is larger than that in the SMA. In order to prevent the damage of thermal shock to the component, the maximum speed is 4℃/s. However, the normal rise rate is set to 1-3℃/s. The typical heating rate is 2℃/s.

2.2 heat preservation section

The heat preservation section is the area where the temperature rises from 120℃-150℃ to the melting point of the solder paste. Its main purpose is to make the temperature of each element in the SMA stable and minimize the temperature difference.In this area, the temperature of the larger components can have enough time to catch up with the smaller components and ensure that the flux in the solder paste is fully volatile. The oxide of the soldering plate, the solder ball and the pin of the element is removed, and the temperature of the entire circuit board is balanced until the end of heat preservation section. It should be noted that all elements on the SMA should have the same temperature at the end of heat preservation section, otherwise, entering the reflux section will cause various bad welding phenomena due to the uneven temperature of each part.

2.3 reflow  section

In this area, the temperature of the heater is set to the highest, which makes the temperature of the component up to the peak temperature. In reflow sectionthe,the different of peak temperature is according to the solder paste to change, the general recommendation for solder melting point temperature plus 20-40℃. For 63Sn/37Pb solder paste with melting point of 183℃ and Sn62/Pb36/Ag2 solder paste with melting point of 179℃, the peak temperature is generally 210-230℃. Reflow time should not be too long to prevent adverse effects on SMA. The ideal temperature curve is the smallest area covered by the “tip zone” of the solder melting point.

DIP, PCB Assembly,Chip Mounter, Pick and Place, IC Mounter, High Speed Mounter, Wave soldering,LED lighting, LED Lamp, LED Display, LED tube,UPS, Power Converter, Power Adepter, Mobile Charger, PCB board handling system, Loader, Unloader, Conveyor,Shuttle, Chip Mounter, Pick and Place, IC Mounter, High Speed Mounter Induction Cooker, AC, Electric Cooker, Fan, TV, Settle Box

Reflow oven process principle and introduction

The reflow oven process principle and introduction

As we know,reflow oven is the most important welding technology in surface mount technology. It has been widely used in many industries including mobile phones, computers, automotive electronics, control circuits, communications, LED lighting and many other industries. More and more electronic devices are converted from through hole to surface mount, and reflow oven  replaces wave  soldering is a obvious  trend in welding industry.

So what is the role of reflow oven equipment in the increasingly mature lead-free SMT process? Let’s take a look at the whole SMT surface mount line:

The whole SMT surface mounting line consists of three parts, such as steel mesh solder paste printing machine, SMT machine and reflow oven furnace. For the machine, and compared with lead free, and no new demands on the equipment itself; for screen printing machine, and a lead-free solder paste in the physical properties there are some differences, so put forward some improvement on the device itself, but there is no qualitative change. the key of lead-free  is  in the reflow oven.

The lead paste (Sn63Pb37) melting point of 183 degrees, if you want to form a good weld must have the thickness of 0.5-3.5um intermetallic compounds in welding, intermetallic compound formation temperature is above the melting point of 10-15, the lead welding is 195-200. The maximum withstand temperature of the electronic device on the circuit board is generally 240 degrees. Therefore, for lead welding, the ideal welding process window is 195-240 degrees.

Because of the change of melting point of lead-free solder paste, lead-free welding has brought great changes for welding process. At present, the lead-free solder paste is Sn96Ag0.5Cu3.5 and the melting point is 217-221 degrees. Good lead-free solder must also be formed 0.5-3.5um thickness intermetallic compounds, intermetallic compound formation temperature is also above the melting point of 10-15 degrees, for lead-free welding, that is, 230-235 degrees. Since the highest temperature of lead-free solder electronic device will not change, therefore, for lead-free soldering, ideal welding process window is 230-245 degrees.
The substantial reduction of process window brings great challenge to ensure welding quality, and also brings higher requirements to stability and reliability of lead-free wave soldering equipment. Because the equipment itself is coupled with the electronic device transverse temperature difference, due to differences in size of heat capacity will produce temperature difference in the heating process, so in the process control of lead-free reflow oven can be adjusted in the process of welding temperature window becomes very small, this is the real lead-free reflow to the difficulty.

 

print soldering flux on the bottom pad of BGA

How to print soldering flux on the bottom pad of BGA

How to print soldering flux on the bottom pad of BGA

In general, Use flux soldering of high viscosity, to splice and process, should ensure that the printing pattern is clear, the overflow flux.

Sometimes,solder paste can be replaced by solder paste, and the metal component of solder paste should be matched with the metal component of solder ball.

When printing, BGA special small template is used. The thickness and opening size of the template should be determined according to the ball diameter and the ball distance.

After printing, the printing quality must be checked. If it is unqualified, it must be printed again after cleaning.