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PCB profiling

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I was curious what others in pcb assembly are doing as far a... - Feb 11, 2015 by Jackg

Funny, I just had this discussion on LinkedIn. Must be the ... - Feb 12, 2015 by robgd3

Thanks for your input Rob, Our operator does not profile pcb... - Feb 12, 2015 by Jackg

You should definitely profile your new BGA containing PCB wi... - Feb 12, 2015 by Evtimov

I'm with Evtimov...if you've got a new assembly with a BGA (... - Feb 13, 2015 by robgd3

What would be a recommended way and were to attach therms fo... - Feb 13, 2015 by Jackg

Drilling a hole, and attaching the thermocouples underneath ... - Feb 16, 2015 by robgd3

A good resource for implementing a BGA assembly process is: ... - Feb 16, 2015 by dyoungquist

Jackg

#73492

PCB profiling | 11 February, 2015

I was curious what others in pcb assembly are doing as far as profiling. Is profiling an important part of the smt process? Should every board type processed be profiled to determine optimum oven temps per paste recommendations.Is it ok to assume that a similar pcb will be ok to run at same temps as one similar. How do these profilers (ex. kic) relate their recorded temps to an actual PCB?

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robgd3

#73499

PCB profiling | 12 February, 2015

Funny, I just had this discussion on LinkedIn. Must be the season.

It is always acceptable and preferably to profile every assembly, if you have the time, resources, and equipment to do it. That is the only way to get the most accurate information on specific assemblies, as thermal mass varies based on component load, copper weight, number of layers, size and type of planes, etc.

With that said, many years ago, a paste company told me that 90% of my boards would run on the same profile, and that I'd only need to worry about the remaining 10%. Time and experience have proven that they are mostly correct.

Similar sized and loaded PCBs, with similar planes and copper weight will mostly run ok on the same profile. That is, until they don't.

How do profilers relate their recorded temps to an actual PCB? Um, well, since they're attached to the actual PCB while recording the temperatures, the answer is pretty self-evident.

Cheers, ..rob

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Jackg

#73501

PCB profiling | 12 February, 2015

Thanks for your input Rob, Our operator does not profile pcb's which so far we have not had issues that could be attributed to his oven settings. We may be running a pcb with a BGA on it and I was concerned about our lack of profiling. I have spent quite a bit of time profiling PCB's especially when we were first setting up our smt line. I lately have not been involved with our current day to day smt operation and I am not sure were our operator gets his oven settings. Also when I say profilers, I was not referring to thermocouples. I was referring to units deemed "profilers" which I did not know actually attached to the pcb. Thanks

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Evtimov

#73503

PCB profiling | 12 February, 2015

You should definitely profile your new BGA containing PCB with a real profiler with attached thermocouples. I would actually drill a hole under the BGA and put a thermocouple there.BGAs usually require longer profiles with longer soaks zone.....and so on. From what I read you are now running on pure luck(or you might be producing boards with questionable quality)

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robgd3

#73517

PCB profiling | 13 February, 2015

I'm with Evtimov...if you've got a new assembly with a BGA (and especially if BGAs aren't an every day occurrence in your process) it should definitely be profiled.

I have run BGA boards without profiling before, and got lucky...but, I wouldn't recommend it. There's too much going on underneath a chip that you can't see to leave it to chance.

cheers, ..rob

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Jackg

#73521

PCB profiling | 13 February, 2015

What would be a recommended way and were to attach therms for profiling on a board with a BGA or BGA's. Evtimov had mentioned drilling a hole and attaching to the BGA? We do not always get sacrificial boards when we do a job. Is attaching to the PCB unpopulated not good. What are you guys recommendations?

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robgd3

#73529

PCB profiling | 16 February, 2015

Drilling a hole, and attaching the thermocouples underneath the part is the recommended way to profile for a BGA, unfortunately. It allows the best method of collecting specific data, including any thermal sinking/shadowing that the BGA creates.

However, I understand that for the most part, you don't get an extra PCB (or, in a lot of instances, an extra BGA). This makes the concept of destructive testing nearly impossible.

So, here's how I've approached it in the past. I've done initial profiling with an existing board, with a thermocouple attached to pads for the BGA. I've then added some additional heat in the reflow area of the oven, or time in reflow. And, then, checked the results.

I've been mostly successful in doing this. However, it's certainly not ideal. For high cost BGA's, and high cost assemblies, it's worth it to work with your customer to create a sacrificial lamb to get the best results.

Cheers, ..rob

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dyoungquist

#73532

PCB profiling | 16 February, 2015

A good resource for implementing a BGA assembly process is:

IPC-7095C Design and Assembly Process Implementation for BGAs

Lots of valuable information in that publication.

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