Reply to: RE>assly:stencil aperture size for 20 mil pitch component Nalin: The other factor to consider is the copper coating on the PCB. If it is HASL, there is less paste volume required, since some solder is already present on the pads. If OSP coatings are being used, I would recommend a full 1-to-1 stencil opening to provide resultant solder to form a reliable solder joint. IMO, I would NOT recommend HASL for SMT designs using 0.020"-pitch components. A FLAT pad surface is a key factor to maximizing assembly yields and minimizing solder bridging or skewed components. Bill Fabry Truevision, Inc. [log in to unmask] -------------------------------------- Date: 11/21/96 9:03 AM To: Bill Fabry From: [log in to unmask] From: Karen Bozynski *** Resending note of 11/21/96 09:17 Process Development Engineering (416) 448-6204 --------------------------------------------------------------- Subject: assly:stencil aperture size for 20 mil pitch component There are additional parameters to consider in aperture design. o Your stencil thickness is your third dimension in determining solder volume, so a thicker stencil would require a smaller aperture (be careful of aspect ratio!), or you could get away with a larger aperture if a thinner stencil is used. o In addition to aspect ratio, the condition of the aperture walls will also determine your success in paste release. You should find good results with laser cutting if your stencil vendor has precise alignment and control of the beam strength. o Your company's SMT process parameters for stencil alignment in the screening stage, module skew in placement, and reflow parameters will also dictate the optimal aperture for you. Good luck! Karen Bozynski Internet: [log in to unmask] Celestica Inc. Phone: (416) 448-6204 844 Don Mills Road, 34/178 Fax: (416) 448-4736 North York, Ontario M3C 1V7 CANADA