Waarom viel het SMT-pad er gemakkelijk af tijdens het solderen van de printplaten??

I am a buyer in a telecom company. Kort geleden, an important order of SMT PCBA is delayed due to insophiscated production of a supplier. I am thinking about replace it and just very puzzled about how did their SMT pad fall off easily when soldering the PCB boards. That slows down the whole process.

Ik vermoed dat dit een handmatige soldeeroperatie was. Hoogstwaarschijnlijk, het strijkijzer was te heet, of het werd te lang op de pad gehouden, of allebei. Als dit laatste, there may have been insufficient flux to enable good heat conduction into the joint, so the operator was forced to keep the iron in place longer than should have been necessary.

The epoxy in the PCB gets distinctly soft above the glass transition temperature(Tg). Guess what? All normal soldering operations happen above the glass transition temperature!

Item Temp.
Traditional FR4 boards Tg: 135C
modern boards for lead-free soldering processes Tg: 170C
Solder melting temperatures for eutectic Tin-Lead (Sn63) 183C
melting temperatures lead-free solders (SAC305) 217C
oldering iron temperature above the liquidus 130C

Facing this problem in soldering operation, all we need to do is making it so fast that there isn’t time for the epoxy to go soft, and that there is no time for the copper pad to lose all adhesion.

En, greater soldering technique should allow the flux to do the work of heat conduction. The soldering iron tip even does not, in feite, touch either component or PCB.

 

In real life, we almost all do allow such contact, but we take care not to exert pressure while doing so. Because undue pressure is what causes pads to fall off if the temperature has gotten too high!

 

Daarnaast, tip condition may be the second factors. Tips, which are badly tinned, stop the heat transfer to the joint. Hierop volgend, many operators have to increase the iron temperature and press the iron into the board hard enough to do push-ups, causing SMT pad falling with ease.

#PCB Assembly #SMT PCB Assembly #PCB Manufacturing

https://www.youtu.be/kX4gCs9szeA?si=F4ehyNfLGBTr8GyG

Picture of Olivier Smit

Olivier Smit

Oliver is een ervaren elektronica-ingenieur met kennis van PCB-ontwerp, analoge circuits, ingebedde systemen, en prototyping. Zijn diepgaande kennis omvat schematisch vastleggen, firmware-codering, simulatie, indeling, testen, en probleemoplossing. Oliver blinkt uit in het omzetten van projecten van concept naar massaproductie met behulp van zijn elektrische ontwerptalenten en mechanische vaardigheden.
Picture of Olivier Smit

Olivier Smit

Oliver is een ervaren elektronica-ingenieur met kennis van PCB-ontwerp, analoge circuits, ingebedde systemen, en prototyping. Zijn diepgaande kennis omvat schematisch vastleggen, firmware-codering, simulatie, indeling, testen, en probleemoplossing. Oliver blinkt uit in het omzetten van projecten van concept naar massaproductie met behulp van zijn elektrische ontwerptalenten en mechanische vaardigheden.

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