Mark,
Appreciate your good analysis!
Lately we have been specifying a .06mm oversize. The board houses we use will do a .05mm oversize (but we try to give them as much as we can) with a .1mm sliver (I have went as small as .075mm, but $$$ go up).
Interesting what the mfgrs are working on for the future. One is working on .038mm SM oversize, and another is working on a .05mm solder mask dam. This is emerging technology, but we can see where they are heading. Cool stuff.
Best Regards
Roger M. Stoops, CID+
Trimble Navigation Ltd., Dayton, OH, USA
Ph: +01 937.245.5288
Fax: +01 937.233.7511
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of Mark
Larson
Sent: Monday, February 02, 2004 10:12 AM
To: [log in to unmask]
Subject: Re: [DC] Regarding Solder Mask Preference
If your pad geometry does not yield at least .1mm solder mask sliver
between pads, they will want gang opening, obviously if you use a gang
opening it will remove the minimum solder mask sliver from
consideration, so most fab shops will prefer the ganged opening, the
real question is what do the assy people prefer?
.5mm centers - .1mm SM sliver = .4mm - .1mm SM oversize = .3mm pad width
.4mm centers - .1mm SM sliver = .3mm - .05mm SM oversize = .25mm pad
width
As you can see, at .5mm it is possible, at .4mm that .05mm oversize is
the killer, .075 is the least I've heard that a shop will reliably do
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Oommen Mathews
Sent: Monday, February 02, 2004 7:26 AM
To: [log in to unmask]
Subject: [DC] Regarding Solder Mask Preference
Hi.,
For fine pitch QFP and SOP components (.5 mm or less) which type of
solder mask is preferred in a fab point of view ? Gang solder mask or
individual pin/pad mask ?
regards,
Oommen Mathews
----------------------------------------------------------
Sr. Engineer - VLSI/System Design,
Wipro Technologies Global R & D,
Tower-4/First Floor/Wing-A,
#72, Keonics, Electronics City,
Hosur Main Road,
Bangalore - 560 100. India
Tel:+91 (0)80 8520408 Ext:4132
Res:+91 (0)80 6659004
email: <[log in to unmask]>
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