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November 2001

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Subject:
From:
Denis Lefebvre <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 19 Nov 2001 10:22:56 -0800
Content-Type:
text/plain
Parts/Attachments:
text/plain (110 lines)
I guess that's a good question for Motorola.
We (designers) have used a "rule of thumb" that says the land size should
be no larger than 1/2 of the ball pitch. Diameter .4mm fits that rule. I
cannot testify as to whether or not it's a good rule... I'm just parroting
what I've been told. We also TEND to follow the manufacturer's
recommendations (when they are given).

-Denis

At 12:42 PM 11/19/2001 -0500, you wrote:
>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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