Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Wave Soldering Moisture Sensitive Devices

Bruce Carnegie

#15141

Wave Soldering Moisture Sensitive Devices | 7 July, 1998

We're running mixed technology boards with moisture sensitive devices on the top side thru our wave machine. Should I be worrying about "popcorning" these devices if they have been sitting out collecting moisture between the application of SM devices and the thru-hole phase of the job? The MS devices were dry packed or baked before reflow so that shouldn't be an issue and the article I've just read seems to indicate that I should be OK in the wave as long as package temp doesn't exceed 180 degrees C, no matter how long the moisture sensitive devices have been "open to the elements". Right or wrong? Any thoughts?

reply »

Steve Gregory

#15143

Re: Wave Soldering Moisture Sensitive Devices | 9 July, 1998

Hi ya' Bruce! If you don't go above 180 degrees C. you should be oakie-dokie...actually the temp limit according to IPC-SM-786A is 220 degrees...and they also detail that statement by saying that's the temperature as measured at the top center of the part. This is just a comment and a question, I was kinda' wondering if anybody has actually had package cracking that they've been able to witness first hand with their own two eyeballs on the floor while it's being built? I ask this because in the 10-years that I've been doing this I never have. Not to say that none of the boards I've built have never had cracked packaging, because I didn't learn a lot about this stuff until after 3-4 years or so working in this industry. But are the cracks ever visible? Or are they always microscopic? Just curious...that's all. -Steve Gregory-

reply »

Bob Willis

#15142

Re: Wave Soldering Moisture Sensitive Devices | 10 July, 1998

As Steve said there should not be a problem with cracking plastic components but if you are reaching 180c there will be a problem with secondary reflow on the top side of the board. PCBs flex during wave soldering as they do during reflow if not supported correctly. | We're running mixed technology boards with moisture sensitive devices on the top side thru our wave machine. Should I be worrying about "popcorning" these devices if they have been sitting out collecting moisture between the application of SM devices and the thru-hole phase of the job? The MS devices were dry packed or baked before reflow so that shouldn't be an issue and the article I've just read seems to indicate that I should be OK in the wave as long as package temp doesn't exceed 180 degrees C, no matter how long the moisture sensitive devices have been "open to the elements". Right or wrong? Any thoughts?

reply »

reflow oven profiler