Hi Alex - I haven't had time to work out the math but MPM has published this formula: Weight of component (in grams)/ Total pad mating area in square inches The grams/square inch must be less than or equal to 30 to keep things from falling off the board. I recommend you run this formula and compare it to a surface tension - force type comparison just to be on the safe side. PS - have you done any Impedance spectroscopy testing lately? Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Surface Tension Author: [log in to unmask] at ccmgw1 Date: 10/5/96 12:05 PM Can someone help me with a formula to approximate my design rules to solve the problem of falling chips on second side reflow. The chips on the second side of the board seem to be to heavy for the superficial tension that is supposed to hold them down while going through the reflow oven for the second time. I want to set PCB design rules depending on the weight of the chip, surface area of the chip's leads and pad sizes. I know that there are many more variables to consider but a simple rule of thumb formula will do. Or if anybody knows about the exact science to deal with this problem I will appreciate the feedback. (Can't use Glue) Thank you much. P.S. This is my first time in ThechNet and I thank you all for the forum. Alex Basauri SMT Engineering Trimble Navigation LTD The GPS Solution!! Sunnyvale, CA [log in to unmask] (408) 736-4924 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************