Yuan Li: It may well be attributed to several items: first, most TBGA's use polyimides whereas very few of the PBGA's would. Next is the use of a power/ground ring in the typical TBGA, as opposed to the discrete power/ground etches or at best power and ground planes. The CTE mismatch of this ground ring, being a horizontal laminar system (as opposed to a compressive vertical structure) would increase the residual stresses at the ball attach. Finally, it is likely that the staircase construction of the TBGA has mismatched CTE's in it (induced by slight variations in the sequntial application of the layers), and these mismatches result in stresses being manifest at the package body and the ball attach. > Bill Davis, Ph.D. > Diamond Multimedia Systems > Senior Scientist > Tel. 408.325.7868 > Cell. 408.888.5650 > e-mail: [log in to unmask] > > -----Original Message----- From: LI YUAN [mailto:[log in to unmask]] Sent: Wednesday, May 12, 1999 12:12 PM To: [log in to unmask] Subject: [TN] BGA Solder joint reliability Dear BGA Reliabilty Experts: I have done FEM simulations for BGAs and have found some results I cannot explain. Hope you can enlighten me on it. I modeled BT-based BGAs and tape-based BGAs (both cavity up) under 0-100C 1 cycle per hour condition. For BT BGAs, with the same die size, the larger the package, the better the mean fatigue life. This phenomina may be attributed to die/package ratio, the bigger the die/package ratio, the worse the fatigue life. However, for tape BGAs (tape substrate is much thinner than BT substrate), the result is the opposite. With the same die size, the larger the package, the worse the fatigue life. Can someone explain why the difference between BT and Tape BGAs? Best regards, Yuan Li ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################