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April 2002

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Subject:
From:
Eric Dawson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 23 Apr 2002 08:18:13 +0100
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text/plain (86 lines)
Hi Steve,
I have not seen this on J leads but definitely under bga.s.
I measured up to 200C under a topside bga* when it went over the wave, so I
reduced the preheat (it was too hot anyway) and used peelable solder mask
under the bga vias. This did the trick but was time consuming.
I was fortunate that I was able to convert the process flow to double side
reflow with pin in hole.
Hope this helps.
Regards
Eric Dawson

* An image has just formed in my mind of a bottom side bga going over a
wave. I think I need to lie down in a darkened room.

> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Tuesday, April 23, 2002 2:07 AM
> To:   [log in to unmask]
> Subject:      [TN] Secondary reflow over wave...
>
> Hi All!
>
> Got a situation here that I think is secondary reflow...
>
> Have a board here that has some J-leaded DRAM that in functional test,
> they
> can get the board to pass test by putting some pressure on top of some of
> the
> 40-pin J-leaded DRAM's that are causing them to fail...
>
> Out of SMT things look fine, but I have observed some boards that have
> failed, show an unusual solder joint appearance after wave. The board is
> "swiss-cheesed" with vias, and none of them are tented. Every pad has a
> via,
> they alternate, some have .050" traces to the pad, some have .020" traces
> to
> the pad.
>
> Where we're seeing problems is where there is a bank of them (like a grid
> of
> 2 by 8 of them layed-out side by side).
>
> I'm thinking secondary reflow because of the open vias...or could be CTE
> mis-match between the part and the board. It's a .062" FR4 board, with
> fairly
> large 40-pin SOJ's, could be experiencing some hellacious mismatch, no?
> The
> gull-wing parts we don't see the problem, even though the via placement is
> the same standard as with the J-leaded parts...J-leads aren't as
> compliant?
>
> Gonna hook-up the mole tomorrow, attaching it to one of the J-leaded parts
> to
> learn what it is seeing...will tell me a lot...
>
> Just wondering if anybody else has run into this before...
>
> -Steve Gregory-
>
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