In reference to the pad layout for the Motorola MCF5272, from many years
of experience in process engineering within a prominent PCB layout design
firm, a pad design of .28mm on this device would warrant extensive process
control to provide for an exceptable yield of soldering this device.
1. This would force manufacturing to perform solder paste stenciling thru
.28mm round apertures.(very difficult)
2. Secondly, If pcb is HASL processed, excess solder could hinder an
already difficult process of paste stenciling.
3. Mechanical reliability of these solder joints would be questionable in
my opinion because of the small surface area provided on the pcb.
4. Component mounting would have to be very accurate and repeatable since
the small surface area on the pcb would decrease the dynamic centering where
BGAs would center on solder reflow.
In conclusion, I think that Motorola recommends approximately .5mm pad
layout and .35mm via pad connections. Our designers would probably follow
what Motorola has recommended and we would require a reputable pcb house
that had good controls over its HASL process or require a different pcb
process that would provide flatter pad surfaces.
Paul Peltier,
Senior Process Manager
----- Original Message -----
From: Denis Lefebvre <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, November 19, 2001 10:42 AM
Subject: Re: [TN] 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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> >
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