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Bottomside smt falling off in wave in only voc-free flux

Vince Gedgaudas

#11051

Bottomside smt falling off in wave in only voc-free flux | 14 June, 1999

Has anyone had issues where bottomside double reflowed smt has fallen off in the wave when using voc-free flux? I have verified the hotter profile was not the issue by using an alcohol based flux with no problems.This voc-free flux is also not causing parts to fall off when just glued to bottomside, only when reflowed! If anyone can help me it would be greatly appreciated.

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#11052

Re: Bottomside smt falling off in wave in only voc-free flux | 15 June, 1999

| Has anyone had issues where bottomside double reflowed smt has fallen off in the wave when using voc-free flux? I have verified the hotter profile was not the issue by using an alcohol based flux with no problems.This voc-free flux is also not causing parts to fall off when just glued to bottomside, only when reflowed! If anyone can help me it would be greatly appreciated. | Vince: Here�s the situation as I understand it:

LIFE IS GOOD: Double sided board, primary side reflowed, and secondary side glued and waved. Second side components are not missing after wave.

LIFE IS BAD: Double sided board; primary side reflowed; and secondary side glued, reflowed, and waved. Second side components are missing after wave.

What�s the same between LIG and LIB boards:

� Adhesive composition, age, deposition, and curing � Reflow solder paste and profile � Wave flux, profile, and set-up

What�s different between LIG and LIB boards:

� Extra reflow step � Boards being processed

Possible explanations are:

1 LIB second side components were missing before they hit the wave, because of:

� Extra handling. See current thread and archives. � Extra handling and embrittlement of adhesive during second reflow cycle.

2 LIB second side components were not missing before they hit the wave, but were after because of:

� Embrittlement of adhesive during second reflow cycle.

Things that make you want to go hummmm?

1 Why is Vince doing all that processing (gluing, reflowing, and waving) on that poor second side of the LIB board? Just what does the second reflow cycle bring to the party? 2 Is something different about the LIG and LIB boards or their processing, beyond the above points, that Vince isn�t telling us? For instance:

� Are the solder mask, it�s cure, and surface finish the same on both boards? � Are the adhesive and its cure on the LIG and LIB boards really the same? � Are the LIB boards from a single lot or from various lots? � Are the LIB boards from a single manufacturer or from various sources? � Is this problem new with a new product? Or is this problem old with an old product? Or is this problem new with an old product? Or some other combination like that?

3 How consistent and widespread is this problem of LIB second side component loss?

Good luck

Dave F

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