How to deal with SMT solder spot yellow cause and improvement measures

The reason:

1. The tin point temperature is too high.

2. Low preheating temperature or fast conveyor belt speed.

3. PCB board or smudgy parts.

Countermeasures:

1. Reduce the temperature of reflux furnace.

2. Adjust the preheating temperature and speed transmission belt.

3.. Responsive supplier improvement

4. Generally, we should confirm what kind of material the board is made of. If the color becomes yellow, we should adjust the furnace temperature, adjust the constant temperature zone, reduce the temperature of the welding zone, generally reduce 10 degrees

5. After welding rosin or colored resin residue exists on the surface of the solder joint, especially the selection of rosin solder paste, although the contrast of rosin flux and free cleaning flux will make the solder joint slightly bright, but the existence of the residue will generally affect this effect, especially in the larger solder joint or IC foot parts more obvious; But after welding cleaning, solder joint glossiness should be improved

pcb

The solder joint is not bright can be roughly considered from the following aspects:

1, the composition of tin paste, tin powder particle size. If the particle is too large or the lack of welding components will cause the solder joint is not bright (the probability of this kind of situation is small, because now famous solder paste products are mostly old products, general manufacturers will not allow the proportion of imbalance of products flow to customers), we recommend the use of double Chile solder paste, we use the effect of comparison!

2, the preheating time is too long. The solder paste stays in the preheating area for too long, and the welding aid components in the meantime are prepaid transpiration, so that the welding aid effect is not good in the real reflux time, forming the solder joint is too dark, and even cold welding.

3, the preheating time is too short and the reflux temperature is low. Brief morning Flux transpiration is incomplete, affecting the appearance of solder joints.

4, the cooling speed is too slow. Generally speaking (just general oh!) Solder joint brightness is proportional to cooling slope.

5. Plan the welding furnace back. Generally, some air-cooled stoves cannot achieve the desired cooling effect, as well as affecting their solder joints.

6, the use of nitrogen, we all know that nitrogen can help welding, but often excessive nitrogen will make the solder joint constitute the effect of secondary oxidation, out of course, the solder joint is not too bright!

7. PCB plan. Such as some large power board (such as power supply class), due to the PCB generally has more large volume components, such components due to more simple heat absorption makes the whole piece of PCB heating uneven, even sometimes dewetting appearance, out of the welding effect of course we can not need too high! However, we can try to improve our furnace temperature by reserving a small way before reflux, so that all components reach the average temperature, and then enter the reflux time together. This effect is better.

The importance of lead-free solder paste in SMT process

SMT technology and process is currently the most popular in the electronic assembly industry. High reliability and strong vibration resistance. Low defect rate of solder joint. Good high frequency characteristics. Electromagnetic and radio frequency interference is reduced. Easy to realize automation, improve production efficiency. Reduce the cost by 30%~50%. Save materials, energy, equipment, manpower, time, etc.

Solder paste is a new kind of welding material accompanied by SMT. Lead-free solder paste is a complex system consisting of a mixture of solder powder, flux, and other additives to form a creamy mixture. Lead-free solder paste has a certain degree of density at room temperature, which can initially stick electronic components in a given position. At welding temperature, with the volatilization of solvent and some additives, the welded components and printed circuit pad will be welded together to form a permanent connection. By changing from manual welding operation to machine patch operation, precision, accuracy and high efficiency are improved. Therefore, the most important auxiliary material in SMT patch, lead-free solder paste, is more and more demanding, and its dependence is more and more strong.

The pace of SMT lead-free process is getting closer and closer. As an important part of lead-free process, the performance of lead-free solder paste has attracted more and more people's attention. As people are more and more demanding of life, the control of all kinds of harmful things that will harm the body is more and more strict. Will continue to introduce the control of harmful substances of various implementation standards, such as: national standards, European Union ROHS standards, WEEE standards, halogen free standards, and these implementation standards will be more and more strict control.

Therefore, the solder paste that must be used in SMT patch process is also changed from the original lead solder paste to lead-free solder paste. And with the continuous upgrading of these standards, the quality and process requirements of lead-free solder paste are more and more strict and attention.