We have found that a method to avoid this issue is to plug prior to LPI
flood coating. The initial plug has a slight raised profile, which is
coated smooth with the finish of LPI, allowing good gasketing at paste.
The results are very smooth and flush to the mask surface. Several of
our customers have written this into their specifications and master
drawings.
Jeffrey Bush
Director, Quality Assurance and Technical Support
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302-1890
Tel. 802.257.4571.21 Fax. 802.257.0011
[log in to unmask]
http://www.vtcircuits.com
-----Original Message-----
From: Black, Paul [mailto:[log in to unmask]]
Sent: Wednesday, September 15, 2004 2:15 PM
To: [log in to unmask]
Subject: Re: [TN] Question about via masking on BGA pattern...
Hi Everyone,
I have a question regarding this issue; my limited experience with
plugging is that it doesn't sit flush at the top of the via but is
somewhat raised. Wouldn't this cause problems printing during solder
deposition?
Thank you,
Paul Black
Manufacturing Engineer
Kronos
E-mail: [log in to unmask]
Voice: (978) 947-1520
Fax: (978) 244-0568
www.kronos.com
Improving the Performance of People and Business(tm)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Charles Caswell
Sent: Wednesday, September 15, 2004 10:59 AM
To: [log in to unmask]
Subject: Re: [TN] Question about via masking on BGA pattern...
I can agree to this. I suggested covering both sides just because most
of our customers question uncovered via's. Not sure why, especially
those with specific notes on drawing to leave via's unplugged and not
masked.
-----Original Message-----
From: Jeffrey Bush [mailto:[log in to unmask]]
Sent: Wednesday, September 15, 2004 7:56 AM
To: [log in to unmask]
Subject: Re: [TN] Question about via masking on BGA pattern...
I would recommmend the opposite of this - plug from the BGA side and
leave the bottom open for testing.
Jeffrey Bush
Director, Quality Assurance and Technical Support
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302-1890
Tel. 802.257.4571.21 Fax. 802.257.0011
[log in to unmask]
http://www.vtcircuits.com
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Wednesday, September 15, 2004 8:44 AM
To: [log in to unmask]
Subject: [TN] Question about via masking on BGA pattern...
Mornin' All!
I have a question about solder masking via's in a BGA pattern, and want
to see if I'm thinking correctly about this.
I think it's a bad idea to leave the via's free from solder mask on the
topside of the board beneath the BGA, and tent the bottomside via's. To
me, you're just asking for trouble down the road because you'll trap
flux residue and all kinds of stuff in the via's that won't be able to
be cleaned out well. This is a 676 ball 1.0mm pitch BGA pattern. Am I
wrong about this?
Thanks!
-Steve Gregory-
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