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Lead and no lead soldering in PCB fabrication

Lead and no lead soldering in PCB fabrication

In the process of manufacturing circuit boards, “exports are lead-free, and domestic lead-made” is often heard. In fact, no good rate can be done very well. From the perspective of social responsibility and long-term reliability, it is recommended that you do lead-free soldering and contribute to environmental protection and sustainable development.
   There is lead and lead-free difference: the lead solder paste has high yield, but it is not environmentally friendly; the lead-free solder paste has a melting point of 220 degrees, and a variety of alloys are formed during the solid phase liquid phase temperature difference, and the welding process window is relatively narrow. After high temperature, the flux loss is too much, and the wettability is poor; the test is more severe for the device, so the lead-free yield control is relatively difficult, and the equipment requirements are higher.
   The devices are now lead-free, and it is suitable for mixed (lead-free devices, lead paste) and lead-free soldering. We prefer to use lead-free soldering for the following reasons:
1. The key to soldering is to melt the solder to form a uniform alloy. If the alloy composition is not uniform, the strength of the solder joint is low and the long-term reliability is poor.


2, the temperature of the mixed control between lead and lead-free, in order to take care of the characteristics of lead solder paste (such as solvent evaporation, activity, etc.) temperature often can not meet the requirements of lead-free solder balls, resulting in lead solder paste After being melted, it is coated on the lower part of the lead-free solder ball which is not completely melted, forming an “egg nest” which is not fully fused. The alloy composition is graded from top to bottom, and the welding strength is not good.
3, the key to mixing is to find a temperature balance point, each manufacturer may be different: no matter what kind of temperature, the problem at the interface can not be completely solved, when the temperature is slightly lower, it is easy to cause cold welding. We have encountered this problem in 0.65 mm BGA soldering: the BGA can be pulled down from the PCB with a little force. The breaking point is mostly between the soldering interface or the solder paste and the PCB, indicating that the strength is really poor: the lead-free of the control The crack of the veneer is distributed on both the PCB and the chip side. The solder balls are often brought along with the pads, and the soldering strength is obviously good.
4. Lead-free devices and lead-free solders are very mature, and achieving high yields is not impossible.
 5. From the perspective of the company’s business, it is also necessary to reserve the lead-free process as early as possible.
6. Based on the above reasons, our products have always chosen lead-free soldering. Although PCB assembly manufacturing yield is slightly lower, the risk is visible and controllable, and the reliability risk of mixing is difficult to judge.
7. The above is just the understanding of our technical team on the mix, the actual industry has a lot of disputes about the mixed view. Our starting point is cost and quality. Please ask the engineers to dialectically, don’t be misled by us.

The above is the industry information provided by FASTPCBA technicians, I hope to help you.

Feb-08-2019

FASTPCBA