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PC Board Guidelines

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PC Board Guidelines | 18 September, 2007

Is there a guideline for the manufacturing of PC Boards? I find that my board changes dramatically from board house to board house, causing about 2% failure rate.

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PC Board Guidelines | 18 September, 2007

Does the change from supplier to supplier as a result of: * Board definition? * Differences in processing at fabs?

3 Specification Fir Tree General Technical Specification 3a Design/Layout: * IPC-2221 * IPC-2222 3b PCB Fab: * IPC-6011 * IPC-6012 * IPC-4101 * IPC-A-600 3c PCB assembly: * J-STD-001 * IPC-A-610

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PC Board Guidelines | 19 September, 2007

Hussman, I'm curious about the same thing.

No offense to some of the people here, but this forum's getting frustrating in terms of the lack of expertise. Too many rookies from foreign countries new to SMT, some of them asking really dumb questions, and when an advanced inquiry like Hussman's does come up, there's only one response, from good ol' reliable DaveF an industry consultant who's been here since the '90s.

Not that it wasn't a good response, but c'mon!

I'm frustrated 'cause I've answered many a reply here, but the inquiries I have put out here (for example I inquired about uBGA's and flipchips) got no replies....sad state of the industry.

I guess the good ones "got smart" and moved on to different types of work when their own jobs got off-shored...

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PC Board Guidelines | 19 September, 2007

Of course there are differences, different equipment, software, tools, etc... We just got a set of questions from a PCB house asking about soldermask clearance between 16 mil pitch pads. Our current manufacturer can put down 3 mils of soldermask. The new house can only do 6 mils and want to know if it is OK to overlap the pads or eliminate the soldermask. Needless to say we won't be using them if they can't meet our requirements.

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PC Board Guidelines | 19 September, 2007

Like davef mentions, there are guidelines for both design and fabrication, not to mention assembly (which from the original post doesn't appear to come into play here).

Not that I could improve on what dave has already shared, but it would be nice to know whether the boards are being designed out of house as well as fabbed. Assuming not, then knowledge of what the failure modes are would help too. Shorts, opens, delam, blisters, what gives?

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PC Board Guidelines | 20 September, 2007

Acualy same supplier, but they have 7 different facilities. Changes in prepreg thickness from lot to lot is the big deal, since internal shorting occurs form time to time. Just wondering if there was a spec I could use to force them to use the same thickness prepreg throughout the board in between layers. A lot of "shoulds" and "shalls" in these documents, peppered with "best manufacturing practices".

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PC Board Guidelines | 20 September, 2007

You can specify the prepreg thickness in the stackup. Once you have specified it somewhere, make your PCB manufacturer build to it... and prove it through cross-section analysis.

Depending on the Board cost, we require a cross-section and analysis done on every lot shipped. We then random sample the cross-section plugs and perform our own analysis to insure we are getting what we want.

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PC Board Guidelines | 20 September, 2007

Are these shorts occuring after reflow, or are they shorted on the incoming boards before stuffing? If the latter, is the fabricator doing electrical test? How are these boards getting past their electrical test? Especially if multilayer, there's no WAY I would stuff a board before SOMEBODY tested it. Finding the short later is just WAY too hard.

I have not run into boards shorting out during/after assembly except in one case over 20 years ago. They obviously had a process problem there, probably leaving contaminants in the board when it was laminated.

I don't have board testing available in-house, so I have to TRUST my fabricator, and I will accept almost any foul-up as long as they make an effort to correct the problem. But, for me, the cardinal sin is to put an ET stamp on the boards without testing. I dumped several board houses over a few years about a decade ago, and NEVER went back to them, EVER, if they pulled that stunt on me, even once. I can tell, under a microscope, if the boards were tested or not, it leaves tiny probe dimples in the pads. I'm glad that the fabricators must have wised up, I'm sure a few much larger customers must have felt the same way I did, and pulling this sort of stunt ought to get you blackballed by any manufacturer.

If definitely good boards are shorting during/after reflow, then you have to compare your processes against what the fabricator guarantees his boards can take. It is a lot less clear where the problem is in this case.


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PC Board Guidelines | 20 September, 2007

Hussman Comments are: * Generally, the "3b PCB Fab:" documents are written by the fabs. Nufsed * There's no reason that you cannot define your boards by specifying the stack [that you learn from the most preferred of the seven shops of your supplier].

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PC Board Guidelines | 21 September, 2007

I've been away for a bunch of years, chasing a different rainbow - all I got to say to SAmir is "Want some cheese with that whine?"

C'mon- this is supposed to be a peer to peer help forum, if I can remember the original intent. Ragging on rookies doesn't help - only makes them afraid to ask "dumb" questions- no such thing as a dumb question, just dumb answers.

Just another dinosaur from the '90's weighing in my humble opinion

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PC Board Guidelines | 26 September, 2007

Hi Hussman,

I have no affiliation to this company, they are actually a competitor of ours,but they have a very good DFM Book on their Web Site that would probably answer some of your questions.

Hope this helps.



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