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October 2001

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Subject:
From:
Steve Owen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 18 Oct 2001 13:46:50 +0100
Content-Type:
text/plain
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text/plain (160 lines)
Larry,

Concerning inspection of BGA's I have just purchased kit supplied by a
company called Ersa. They use a form of endoscope that is able to look
between the pcb and the underside of the BGA between the rows of solder
balls. To check if the device has reflowed properly. It also comes with an
extensive fault library wihin it's software.

-----Original Message-----
From: Bill Raymond [mailto:[log in to unmask]]
Sent: 18 October 2001 13:08
To: [log in to unmask]
Subject: Re: [TN] double sided BGAs


I've done up to 35 mm packages (PBGA) with 492 balls, 1.27 mm pitch... the
surface tension was plenty to hold them in place.

Bill...


At 10:51 AM 10/18/2001 +0800, you wrote:
>..........................................................How big are the
>BGA's? It's
>possible that they're light enough for surface tension to hold them in
>place while up-side down during the second solder pass without them falling
>off. Steve Gregory, I think it was, once gave a figure of how much weight
>per contact can be held in place by surface tension of molten solder - was
>it 5 grams per contact? But I don't know if this figure can be applied to
>BGA's with their all-solder contacts. The effects of gravity and other
>forces may distort the solder joints' form enough to reduce their
>reliability.
>
>My tuppence worth (UK value), but hope it helps a little.
>
>Peter Duncan
>
>
>
>
>                     Larry Koens
>                     <lwkoens@EIMI        To:     [log in to unmask]
>                     CRO.COM>             cc:     (bcc: DUNCAN Peter/Asst
> Prin Engr/ST
>                     Sent by:             Aero/ST Group)
>                     TechNet              Subject:     [TN] double sided
BGAs
>                     <[log in to unmask]
>                     ORG>
>
>
>                     10/18/01
>                     12:32 AM
>                     Please
>                     respond to
>                     "TechNet
>                     E-Mail
>                     Forum."
>
>
>
>
>
>
>Dear TechNet,
>My company has been  asked to bid on assembling a board that would have
>two BGAs on the topside and two more BGAs mirrored on the bottomside.
>That is, they will be directly across from each other on both sides. I
>never done them on both sides. So far, everything that I have done has
>been on one side only. Has anyone done them on both sides before?
>
>   I am figuring xray will be a problem as after the second side is
>placed, because the pads/balls will mirror each other on both sides.
>Would I be able to tell the difference between the two BGA connections?
>Suggestions?
>
>Will I need to epoxy the first side BGAs so they would not drop off
>during my second reflow? Wouldn't I need to epoxy them after first
>reflow so that the balls could collapse?
>
>Thanks,
>Larry Koens
>SMT Manufacturing Engineer
>E.I. Microcircuits
>Mankato, MN
>
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