Martin, In my experience the problem with the solder paste building up on the underside of the stencil is initially caused by poor gasket of stencil to board. This can either be due to poorly finished PCB's or oversize or poorly defined apertures. With regard to your underside cleaning issues, sometines the solvent used in the underside cleaning unit can have an adverse effect in drying out the small quantity of solder paste on the underside of the stencil very quickly. This accompanied by poor undersceen cleaning performance can result in a very quick build up of solder paste. The best advice I can offer is to look at the optimisation of the underscreen cleaning unit including the paper being used and the solvent in the tank. The other area to look at would be the gasketing of the board against the PCB. Look at the aperture size and finish in the stencil. Have the apertures been reduced correctly in line with the PCB pads? I hope this is of some help. If I can be of any further assistance please do not hesitate to contact me. Doug Black Technical Manager Dek Precision Screens Division Dek Printign Machines Ltd. e-mail: [log in to unmask] ---------- From: Martin, Jesse To: [log in to unmask] Subject: [TN] Solder paste stencils Date: 16 August 1999 20:08 Has anyone had a problem with solder paste stencils that have a build up of solder paste on the bottom (PCB) side of the stencil that won't come off in the stencil cleaner? I think what happens is the vacuum/paper wiper leaves some on the bottom after each wipe and the more it wipes the harder it is to get off. I can pop it off with an Xacto knife or the like but is very time consuming. Only other thing that works is using a Scotchbrite pad but that leaves a lot of scratches (which probably causes faster build up). Have also tried stainless steel cleaner with no luck. We use an old Austin American batch aqueous cleaner with saponifier at 120 degrees F. Any and all ideas welcome. ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ############################################################## ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################