Ted, Count 1 vote for using high Tg materials on any design meeting the following criteria: - 50+% overall resin content - 0.093+" thickness - Qty: 10,000+ vias .0135" dia. or smaller My PTV reliability simulation shows a little over 2x MTBF for 170 Tg mat'l vs. 140 Tg (all other factors being equal). It's difficult to predict actual board failure probability - it's a messy Weibull distribution... But, as I'm sure you know, the resin's CTE increases by 15-20x above it's Tg which imparts added tensile stress to the barrel for the duration of the reflow profile, solder wave, etc. This corresponds to a little more elastic strain on the copper barrel, but considerably less plastic strain (i.e., deformation, which if severe enough, causes fracture). All formulas in this simulation program are based on IPC-TR-579 - a great resource. Joe Felts PC World, Toronto ______________________________ Reply Separator _________________________________ Subject: DESIGN: Aspect Ratio versus Material choice Author: [log in to unmask] at INET Date: 2/20/97 7:06 AM We are redoing our specification and are wondering if anyone has design guidelines that take into account either aspect ratio (or drilled hole size) and choice of material into account. For instance on a 0.125" board with a 0.0135" hole( ratio 9.4), or a 0.093" board with a 0.0135" mil hole(ratio 6.9) do you specify to the designer use of a higher glass transition material that you do on the same hole size on a 0.062" ( ratio4.6)? An example would be polyimide for the 0.125 thickness, multifunctional for the 0.093 thickness and standard FR-4 for the 0.062 thickness or a chart that shows increasing thickness or aspect ratio versus what material should be used. Anybody have any thoughts on this or comments? Or is there any fabrication industry consensus? Thanks in advance for your inputs; [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************