Hi Ed! Let me throw a different perspective at you. With proper process
control of my solder stenciling process I don't need to rely on a
soldermask dam to prevent bridging on fine pitch pads and the absence of
soldermask dams on the fine pitch pads gives the board fabricator a larger
process window. I agree that a board fabricator should be able to put the
soldermask dams in place but if I can make the board fabrication operation
simpler then I should get  cost and yield improvements.  Just a different
perspective.

Dave Hillman
Rockwell Collins
[log in to unmask]




Ed Valentine <[log in to unmask]>@IPC.ORG> on 09/01/2000 07:52:19 AM

Please respond to Ed Valentine <[log in to unmask]>

Sent by:  TechNet <[log in to unmask]>


To:   [log in to unmask]
cc:

Subject:  Re: [TN] Soldermask Between QFP pads?


Rick -

I must respectfully disagree with some of the comments from some of my
colleagues. First of all, a board fabricator should not have difficulty
with
solder mask between the pads on 20-mil or even 16-mil pitch these days. In
the late 80's, at the company I was then, we went through extensive testing
on in-house-designed test boards using dummy components with both windows
and LPI mask between the pads, and we had much higher yields with the mask
between the pads. The process is more robust and gives you a wider process
latitude.

Ed Valentine
Electronics Manufacturing Solutions
8612 Mourning Dove Road, Raleigh, NC 27615
Phone: (919) 270-5145, Fax: (919) 847-9971
Email: [log in to unmask]
Website: http://www.ems-consulting.com

----- Original Message -----
From: "Rick Thompson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 31, 2000 7:31 PM
Subject: [TN] Soldermask Between QFP pads?


> Hi,
>
> We have a customer who has a board with 20 mil pitch QFP's on it.  The
> actual pad size is 11.8 mils wide and there is a 2 mil gap in the
soldermask
> around the pads leaving 4.2 mils of solder mask between the pads.  The
board
> house that is building these says they can't maintain the soldermask
between
> the pads and is asking for a window around all leads in the group or a
> tightening of the soldermask openings around the pads.  Before I go to
our
> customer with this, I'd like to get some feedback on whether or not this
is
> unreasonable?  Are these dimensions acheivable or should I ask our
customer
> for a deviation?
>
> Thanks in advance,
>
>
> Rick Thompson
> Ventura Electronics Assembly
> 2665A Park Center Dr.
> Simi Valley, CA 93065
>
> +1 (805) 584-9858 voice
> +1 (805) 584-1529 fax
> [log in to unmask]
>
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