We have been building Immersion Silver boards for two years now. They are
the best thing since sliced Lead. All Protos are done in silver if they have
one fine pitch device. We are contract mfg. so we see a lot of different
designs.

We started out with 1:1 apertures, concerned that the loss of the solder on
the pads not being a HASSLE board would create insufficient solder joints.
That worked fine until you got to 20 mil pitch. Then you had to reduce the
apertures by 10% to avoid shorting. Then we discovered the joys of resistor
networks. We have worked our way through several Readme.doc variations and
have settled successfully on this when board is I.S.


All SOT23's apertures to be reduced 10%,
Homeplate all R's and C's,
All IC's round rectangle the apertures
Any aperture larger than .200 must be crosshatched (windowpane)
20 and 25 mil components reduce by 1 mil each side of aperture
31 mil and higher do not reduce less than 1.5 times stencil thickness
(.009.)
0201, 0402 and resistor networks are not to be reduced

For BGAs we actually improved our solderability on, we go with a square
aperture with a rounded corners and
for .030 ball reduce to .026 square with round corners
for .024 ball reduce to .020 square with round corners
for .018 ball leave at .018 square with rounded corners
for .014 increase aperture to .016 square with round corners
for .012 increase aperture to .014 square with round corners (look at
electroforming stencil for better release at that point)

We used this for .005 as well as .006 thick laser cut stencils with electro
polishing.
Dave Chapman
Manufacturing Engineer
Circuit Service Inc.

-----Original Message-----
From: Carlr Ray [mailto:[log in to unmask]]
Sent: Tuesday, July 08, 2003 4:55 PM
To: [log in to unmask]
Subject: [TN] Stencil considerations for Immersion Silver


Hello all,
 I am working with a customer who wants to try immersion silver
finishes on their products. I would like to ask the Technet Community
for some suggestions for stencil designs.
 The products vary in complexity and size but nothing "freakish". The
board are have fine pitch (nothing lees than 16 mils), FPBGAs, lots if
PTH devices and 0402s.
 Any ideas people???

Carl Ray
Sr. Manufacturing Engineer
Huntsville, AL 35807
Phone: 256-882-4800 ext. 8845
Cell: 256-990-1990

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