The delta Tg is regulated in PCB manufacturing spec., but for IC substrate there is not any spec. include this item. It is often 2-4 deg C. Also I found the delta Tg measurement methos in IPC-TM-650 2.4.25. The IPC spec. suggest that not apply this method on BT, polyimide materials, because they may increase Tg further during measurement procedure. However, I measured the delta Tg of substrate which made by BT core (4 layer substrate). The delta Tg is roughly 20 deg C in the first time. The second run on the same sample is down to 4-6 deg C, and get smaller and smaller for 3rd and 4 th run. My questions are: 1. How can we know the curing extent of BT will noe affect the IC package reliability? What is the best delta Tg we can accept, after substrate manufacturing and after IC assembly? 2. Does anyone knows any spec. or any substrate supplier have this regulation? If you have any question or further discussion, please let me know. Enigma P. --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------