The rule of thumb, as I understand it, is 80% of the smallest ball size or
preferably the same size as the substrate land. The object being to control
the collapse of the solderball.
If the minimum ball size is 0.35mm, how can you (or Mortorola) justify a
pad size of 0.4-0.5mm?
At 10:40 AM 11/19/01 -0600, you wrote:
>Date: Mon, 19 Nov 2001 07:42:59 -0800
>From: Denis Lefebvre <[log in to unmask]>
>Subject: Re: TechNet Digest - 18 Nov 2001 to 19 Nov 2001 - Special issue
> (#2001-713)
>
>As a layout designer, I am surprised that they used such small land areas.
>Motorola recommends a land of .40 to .50mm. IMO .28mm is insufficient.
>See attached PDF from Motorola.
>
>Denis Lefebvre, C.I.D.
>Senior PCB Designer
>Finisar Corporation
>(408)542-3832
>http://www.finisar.com
>
>At 10:16 AM 11/19/2001 -0500, you wrote:
> >I'm not that far up in the food chain to know all of the particulars, but
> >it wouldn't surprise me if that were the case.
> >
> >What I'm looking for is comments on the increase of pad size and
> >corroboration in my belief that it's the wrong solution to this problem.
> >
> >Tom
> >
> >At 04:20 AM 11/19/01 -0600, you wrote:
> >>Date: Mon, 19 Nov 2001 08:20:31 -0000
> >>From: Eric Dawson <[log in to unmask]>
> >>Subject: Re: BGA bone of contention
> >>
> >>Hi Tom,
> >>Are you wave soldering the other side of the board with the reflow soldered
> >>bga.s on top? I have come across this practice and it definitely disturbs
> >>the bga joints causing opens which cannot be detected by ordinary X ray
> >>inspection.
> >>Hope this helps.
> >>Regards
> >>Eric Dawson
> >>
> >> > -----Original Message-----
> >> > From: Tom Colby [SMTP:[log in to unmask]]
> >> > Sent: Friday, November 16, 2001 8:47 PM
> >> > To: [log in to unmask]
> >> > Subject: [TN] BGA bone of contention
> >> >
> >> > Help me out with this technetters,
> >> >
> >> > The problem: BGA opens on a HASL board.
> >> >
> >> > The device: Motorola MCF5272, a 196 MAPBGA, 1mm pitch, ball size of
> >> > 0.35/0.65. Substrate land size unknown. Footprint designed with a
> pad of
> >> > 0.28mm.
> >> >
> >> > Management's solution is to increase the pad size to 0.4mm. I say to
> look
> >> > elsewhere in the process for the problem.
> >> >
> >> > I'd like to hear the opinions of my esteemed colleagues. What do you say
> >> > folks?
> >> >
> >> > Thanks in advance,
> >> >
> >> > Tom
> >> >
> >> >
> --------------------------------------------------------------------------
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