Steve,
I have to be awkward and ask by how much?
This would be with reference to today's board and mask materials and paste formulations.
In the eurotrash zone, at least, 3mil mask to copper spacing is the norm, and one can expect to get all sorts of objections when
specifying an delivered minimum gap of 1mil. Quite a few fabs are still curtain coating. Some go immediately for the largest
panels even when the order volume would only equate to say 5 or 10 panels worth.
Having just said that, quite a few of these same fabs will also accept HDI work, and do it well!
Best Regards
David Greig
______________________________
GigaDyne Ltd
5 Albany Business Centre
Gardeners Street
Dunfermline KY12 0RN
United Kingdom
t: +44 (0)1383 624 975
www.gigadyne.co.uk
______________________________
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: 16 February 2007 15:37
To: [log in to unmask]
Subject: Re: [TN] LPI soldermask resolution
Hi David,
It's been my experience that having mask between the pads does help to prevent solder bridges. I think it helps the solder to
coalesce back to each pad when it is liquidous during reflow, and helps with gasketing of the stencil during solder paste
printing. That doesn't mean that it's absolutely necessary, but it does help in my opinion. That's why the term "solder mask
dam" is sometimes used to describe the strip of mask between the pads.
If an LPI mask is used, I would prefer to see mask between the pads...
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Greig
Sent: Friday, February 16, 2007 9:17 AM
To: [log in to unmask]
Subject: Re: [TN] LPI soldermask resolution
Hi list,
I want to ask what may well be a silly question -
Why is having a strip of soldermask between the pads of fine pitch
(~20mil) IC's so important?
Best Regards
David Greig
______________________________
GigaDyne Ltd
5 Albany Business Centre
Gardeners Street
Dunfermline KY12 0RN
United Kingdom
t: +44 (0)1383 624 975
www.gigadyne.co.uk
______________________________
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
Sent: 16 February 2007 00:45
To: [log in to unmask]
Subject: Re: [TN] LPI soldermask resolution
Hi Steve,
I am accustomed to thinking of LPI soldermask as a +/- .003"
material....and for that reason we try to discourage designers from trying to have dams less than .006" wide.
Having said that, I will admit that it is my preference is to not use soldermask on certain 20 mil pitch components such as
BCC48, yet we do use soldermask on BGAs at the same pitch.
I will assume you are talking about stripes (dams) between the pads for a gull wing QFP leads, and yes, the resolution of LPI
allows any good pwb fabricator to put a 6 mil wide or larger dam between the pads.
Now if your pads are equal or greater than 14 mils, then the yield at the fabricators will be impacted.
Hope this helps,
Phil
12/2007 -0600, Steve Gregory wrote:
>Mornin' All!
>
>What kind of resolution should a LPI be able to give you? Specifically,
>LPI's should be able to give you a solder mask dam between 20-mil pitch
>leads if you have 8-mils of space between the pads shouldn't it?
>
>Thanks!
>
>-Steve Gregory-
>
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