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January 2003

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 29 Jan 2003 11:12:37 +0000
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> Hi,
> 
>  I'm just wondering if someone could answer this silly question...we have
> on a board some BGA and other discretes components, when we look at the
> X-Ray picture we see that we have void (flux entrapment),  We look at our
> BGAs and there are no trace of void before we pass it to the oven.  Our
> finnish is a Tin Lead the surface is not flat( HASL), we check our profile
> and everything is perfect.  Could our void could came from the finnish? like
> this is not a flat surface could we find a void in the pad?? I know this
> sound silly but I really don't see where those voids could came of.
> 
> We didn't pass a empty board on the X-ray.
> 
> 
> Thanks You
> 
> Yannick Brisson

Yannick

I have awaited other responses, in case I was missing something. However, I
suspect that you "problem" is related to reflow characteristics.

Using conventional convection reflow, in order to ensure a suitable
temperature profile is achieved on the BGA balls on the "interior" bumps,
you have to "over-cook" the outside bumps.

Such "over-cooking" might cause the problem you mention?

The easiest way to overcome this problem is to use vapour phase - or
"Condensation Soldering" to give it its modern term. The benefit being that
you achieve a uniform temperature over all surfaces and in this way, control
the over-temperature to a maximum of 5DegC over eutectic / melting.

Can I provide more on the equipment? Just ask - but off-line please!

--
Regards, Graham Naisbitt
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