We swell the soldermask 1 mil over the pad geometry for 20 mil (19.685
mil)(.5mm) pitch QFP's, leaving just under 6 mils, (5.874mils) (.1492mm)
nominal,  of soldermask between the pins... this helps to prevent bridging
between the pins... also we changed from using HASL to OSP for our boards
and the assembly house loves us. (For caps, resistors, etc....everything
else on the board,  we swell the soldermask 4 mils. )
Protel's DFM rules make it possible to set these features down to the single
pad on the part...
- Bill Brooks


-----Original Message-----
From: Jorge A Rodriguez [mailto:[log in to unmask]]
Sent: Wednesday, July 19, 2000 1:07 PM
To: [log in to unmask]
Subject: [TN] Solder mask clearance


Fellow technetters,
               Can someone help me to find out what's the maximum clearance
on all sides of pads for a HASL board on a 20 mil pitch QFP. We are having
bridging problems with this device and we are suspecting  of the solder
mask between the pads. Currently the PWB we are using shows 10 mils pads
followed by a clearance of 2.5 mils and then 5 mils of solder mask. Also
what is a normal thickness of the plating on a HASL board?



               Any information will be appreciated



Jorge A Rodriguez
Process Engineer
Conexant Systems Inc

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