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Bare PWB bake out during circuit assembly

Russ Cutler

#8664

Bare PWB bake out during circuit assembly | 5 November, 1999

We recently came to a cross roads...

We have historically baked out ALL of our circuit cards, with a 2 fold purpose 1) to dry the part marking ink, and 2) to eliminate any moisture, which could result in measling further in the process of assembly.

We have implemented barcode labels on a lot of cards, which eliminates the need to bake strictly to cure the wet ink.

Is there any technical reason we should maintain the bake out process even though we place barcode labels on the cards?

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chartrain

#8665

Re: Bare PWB bake out during circuit assembly | 5 November, 1999

Amazing in today's technology that people still bake because "that's the way we've alawys done it". Baking is a band aid for poor manufacturing of the PCB. Moisture can become trapped between the layers during buildup. This moisture when it contacts molten solder instantly turns it into steam. The steam seeks the path of least resistance, typically plated through holes with poor barrel plating. Next thing you see is Old Faithful the blowhole. Baking was perceived to be a stop gap measure. Many manufacturing specs will call for baking at the correct temperature for the appropriate time???? baking further oxidizes the solderable surfaces which doesn't sit well with no clean fluxes. Try not baking - you may be pleasantly surprised. Bob Willis has a non destructive test to prove out the moisture in the board.

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#8666

Re: Bare PWB bake out during circuit assembly | 8 November, 1999

Believe it! Although it might be necessary in certain rare cases, and as Ray says, as a bandaid, to routinely bake your boards is a mistake. For much more info, search the IPC technet archives over the last few weeks. It was a popular thread

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Boca

#8667

Re: Bare PWB bake out during circuit assembly | 10 November, 1999

Generic fabs should not require baking. Some special cases like teflon and flex circuits take moisture very well, they often continue to require a trip to the oven. Best wishes, Boca

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