Kelly, We also assemble PWA's that have fine pitch parts(.5mm), that are 12+ layers, aprox. 350X400mm, and 20mm thick. Our experience is that there is inherently some dimensional instability in boards this big when fabricated with FR4 and FR5. We generally see some GROWTH in at least one of the axis on these boards. I haven't experienced a problem with the boards actually being smaller or shrinking. You're right! This problem is most challenging at our solder printing operation. Although we have not actually measured the growth, it's in the area of .127mm (.005")max. in either the X or Y dimension. Our stencils are stainless steel and are produced with no compensation for shrink or growth in the PWB. We have been dealing with this by compromising the solderpaste print registration, and splitting the difference across the board. As you indicated the problem gets worse at the extreme outside edges of the board. At component placement, we are using local etched fiducials to optimize component lead to pad registration. We do see some solder bridging as a result of the solder paste deposits being slightly off the pads. I am interested in hearing from the Board Fabricators as to what they feel is reasonable and possible at their end in helping us deal with this problem. Dan Botts Hughes Training Inc. Binghamton, NY ______________________________ Reply Separator _________________________________ Subject: PCB vs. Paste Stencil Comp Author: [log in to unmask] at CCGATE Date: 10/18/95 4:08 PM From: Kelly Kovalovsky, PCB Quality Engineering ~ EMail:[log in to unmask] Subject: PCB vs. Paste Stencil Comp We have a fairly large circuit board that we are assembling. The card has fine pitch SMT at extreme ends. We have noticed a mismatch between the solder paste stencil and the printed circuit board. The circuit board features are actually closer together than the stencil. My question to any card assembly site is whether it is common practice to compensate a solder paste stencil for shrinkage of a PCB? IBM Microelectronics Division 6800 IBM Drive MG12/251 Charlotte, NC 28262-8563 The following is an attached File item from cc:Mail. It contains information that had to be encoded to ensure successful transmission through various mail systems. To decode the file use the UUDECODE program. --------------------------------- Cut Here --------------------------------- begin 644 rfc822.txt M1G)O;2!I<&,A:7!C+F]R9R%496-H3F5T+7)E<75E<W1`=W=A+F-O;0T*6"U% M;G9E;&]P92U&<F]M.B!I<&,A:7!C+F]R9R%496-H3F5T+7)E<75E<W1`=W=A M+F-O;0T*4F5C96EV960Z(&9R;VT@;6ES;RYW=V$N8V]M("@Q.3@N-#DN,3<T M+C,S*2!B>2!%1$5.+DA!0RY#3TT@*%!-1$8@5C0N,RTW(",U.#@T*0T*(&ED M(#PP,4A73$(S0DI964\P,$,W1$%`141%3BY(04,N0T]-/CL@5V5D+"`Q."!/ M8W0@,3DY-2`Q-CHP.#HS-"!04U0-"E)E8V5I=F5D.B!F<F]M(&EP8R!B>2!M M:7-O+G=W82YC;VT@=VET:"!U=6-P("A3;6%I;#,N,2XR."XQ(",X*0T*(&ED M(&TP=#5H86DM,#`P:6990SL@5V5D+"`Q."[log in to unmask]@,3@Z,#@@0T14#0I2 M96-E:79E9#H@8GD@:7!C:'$N8V]M("A3;6%I;#,N,2XR."XQ(",R*2!I9"!M M,'0U:$9*+3`P,#!(-$,[(%=E9"P-"B`Q."[log in to unmask]@,3<Z-#8@0T14#0I$ M871E.B!7960L(#$X($]C="`Q.3DU(#$X.C(Y.C$Q("TP-#`P("A%1%0I#0I2 M97-E;G0M9G)O;3H@5&5C:$YE=$!I<&,N;W)G#0I&<F]M.B!K:V]V86QO=G-K M>4!V;F5T+DE"32Y#3TT-"E-U8FIE8W0Z(%!#0B!V<RX@4&%S=&4@4W1E;F-I M;"!#;VUP#0I297-E;G0M<V5N9&5R.B!496-H3F5T+7)E<75E<W1`:7!C+F]R M9PT*5&\Z('1E8VAN971`:7!C:'$N8V]M#0I297-E;G0M;65S<V%G92UI9#H@ M/"):<6=C-3$N,"YS,S@N1D5/6&TB0&EP8SX-"DUE<W-A9V4M:60Z(#QM,'0U M9WIB+3`P,&E1;T-`;6ES;RYW=V$N8V]M/@T*0V]N=&5N="UT<F%N<V9E<BUE M;F-O9&EN9SH@-T))5`T*3VQD+5)E='5R;BU0871H.B`\;6ES;R%V;F5T+DE" M32Y#3TTA:VMO=F%L;W9S:WD^#0I8+4UA:6QI;F<M3&[log in to unmask] M:7!C+F]R9SX@87)C:&EV92]L871E<W0O,30Q-0T*6"U,;V]P.B!496-H3F5T <0&EP8RYO<F<-"E!R96-E9&5N8V4Z(&QI<W0-"@`` end