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No Clean in High Frequency Apps

EFData

#13319

No Clean in High Frequency Apps | 9 December, 1998

Does anybody out there have any special insights into utilizing no clean paste in high frequency RF applications? I would imagine there may be some issues with solder balls that would affect functional test (Earl, do you have something for me here?) We currently aqueous clean our RF pcbs, but we are looking to squeeze cycle times.

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Earl Moon

#13320

Re: No Clean in High Frequency Apps | 9 December, 1998

| Does anybody out there have any special insights into utilizing no clean paste in high frequency RF applications? I would imagine there may be some issues with solder balls that would affect functional test (Earl, do you have something for me here?) We currently aqueous clean our RF pcbs, but we are looking to squeeze cycle times. | Hi EFData folks! How's everything in the Great Southworst?

Solder balls and RF can cause inconsistent problems in functional test and operation, as you have stated. Solder balls normally are not static. Those not embedded in uncured solder mask, continually move to cause problems on all board types. One obvious problem would be shorting. For RF, you know better than me the "delicate" nature of the beast as incosistent performance (spikes that change location and value daily, etc.).

The key is to design product not allowing solder ball, or any other defect, formation. Easy to say.

I'm not saying this as a negative comment. You folks know how difficult it is to design RF stuff to look like like normal high speed stuff and still perform as calculated or specified. Almost every time I work with RF, there are designs that are difficult to solder with any type flux or process.

I worked with a company last year to resolve very serious solderability issues concerning solder balls, excessive touch up, component cracking, and solderability in general. We redesigned most boards with fairly "standard" design rules to eliminate excessive heat sinking and solder drain off down holes in pads to eliminate touch up. Also, we went to Ni/Au as an alternative to HASL. Neckdowns also resolved some issues but for the ones negatively impacting electrical performance though some re-calculating resolved this issue where possible.

As far as no clean goes (with RF), we went nitrogen to minimize solder balling. VOC free, no clean presents its special problems, as you know. First, we retrofitted a wave solder machine with air knives after flux application to minimize the problem. Then, we retro'd with nitrogen with semi-acceptable results. The best results were gained in factory nitrogen equipped machines for both wave and reflow.

I know you know - cleaning solder balls is not fun or efficient if even possible at times. I really haven't said much here, but for prevention any way that works - either at the design level or during solder processing with better atmospheres (inert) or better profiles, or both.

I really wish you well with RF as most everyone will face similar problems even with more standard stuff in the very near future when no-clean and VOC free no-clean becomes part of everyday life. Really looking forward to lead-free with those flux types.

Best regards,

Earl Moon

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