Steve,
My pads are similarly oriented. Typically my pad width matches the chip
width.
We are homeplating because of excess solderball generation. It is
something that became more prevalent recently with current formulations of
no-clean (leaded) solder pastes that we were getting. Our screens are anywhere
from 5mil to 7 mil thickness depending on the assemblies. We are homeplating
all chip components that do not have some form of relief (i.e. SMB or SMC
devices, some molded devices have relief areas, troughs, around the contact
where the solderpaste is not squished between the contact and the part body)
around the pads/contacts. Our SMT people tried a lot of other solutions and
consulted with the paste supplier extensively, the only workable solution we
found was the homeplating. Of course being a SMT production issue it could have
contributing factors from many sources during processing.
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
#14 - 1925 Kirschner Road,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
-----Original Message-----
From: Steve Allen [mailto:[EMAIL PROTECTED]
Sent: Thursday, January 12, 2006 10:45 AM
To: Protel EDA Discussion List
Subject: Re: [PEDA] 0402 Land Pattern
Brad,
Thank you.
It looks like my pad might be rotated 90deg from yours. The long
side of my pad (0.6mm) is parallel with the long side of the
part. Is yours the same?
Our manufacturing engineer helped me understand the homeplate
process. I'd never encountered it before. He remembers this being
more prevalent in the early 90's with IR soldering. Why do you use
homeplate? Do you use lead free paste / bare board plating? Do you
only use homeplate with 0402's? What's your stencil thickness? Ours
is 0.006in thick and paste is applied with with a single blade steel squeege.
Thanks again,
Steve
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