Darrel, This is a difficult area in dealing with bakeout before rework. If you want to treat the board and part 'by the book' according to J-STD-033, Table 2, you have two choices. The first is a high temp bakeout at 125C between 4 hours and 48 hours, dependent upon the package thickness and moisture sensitivity level of the part. As you have seen, many through-hole or second ops parts don't like this temperature very much, creating more rework than originally planned for. Your second choice is a low temp bakeout at 40C, which will cause you a different sort of grief based on a bakeout time of between 5 days and 68 days. Not very conducive to rapid turnaround of repair boards. Many folks develop their own criteria, trying to find a 'happy medium' between time and temperature, based on the requirements of the temperature sensitive parts such as through-hole stuff. I have seen 90C for 48 hours used before by others. The primary purpose of bakeout before rework is to prevent additional damage to the part being removed to allow for proper failure analysis by the vendor. The secondary purpose of minimizing potential damage to the substrate during rework can be achieved with lower temperatures and shorter times. However, if you can keep your external component temperature under 200C baking may not be required at all. J-STD-033 covers this in Section 8.6: 8.6 Board rework If packages are to be removed from the board, it is recommended that localized heating be used and the maximum body temperature excursion of any surface mount component not exceed 200 °C. This method will minimize moisture related component damage. If the component temperature exceeds 200 °C, the board may require a bakeout prior to rework. The component temperature shall be measured at the top center of the package body. If the part is to be reused, it is recommended that it be baked dry before remount. Replacement components shall not have exceeded their specified floor life. Localized replacement reflow heating is recommended, so that the entire board is not re-subjected to reflow temperature profiles. You can download a copy of J-STD-033, along with many other useful standards, at www.jedec.org <http://www.jedec.org> . Mike McMonagle Senior SMT Engineer Telxon Corporation www.telxon.com <http://www.telxon.com> -----Original Message----- From: Darrel Therriault [mailto:[log in to unmask]] Sent: Friday, October 13, 2000 9:59 AM To: [log in to unmask] Subject: Re: [TN] Baking PWA before BGA rework Charles, Good question. I just recently had some boards baked at 125c for 24 hours to do BGA replacement only to find when they came out of the oven that the shrink wrap on several electrolytic caps had cracked and peeled. I found the upper operating environment for the caps was stated at 85c, although I don't believe that means it is the max temp they can stand. The spec sheet did not indicate a max temp for prolonged periods (e.g. bake time) other then to provide an assembly thermal profile, which had ramp/dwell time at around 150 seconds and max temp around 260c for 30 seconds. I hope I missed something in the data sheet that will shed some light on this spec, as we rework BGAs often and I don't want to be destroying or degrading anything on the board. Regards....DT At 09:34 AM 10/13/00 -0400, you wrote: >Hello TechNetters! > >I am interested in the baking parameters being used for assembled PCBs >prior to BGA rework in order to reduce risk of moisture-related damage. > >Component vendors often suggest 125'C for 24 hours, but this is based on >component level requirements for drying out unmounted components. I >have heard of baking assembled PCBs at 90'C for 48 hours. > >Your input is most appreciated. >Charles. > >-- >Charles Elliott, P.Eng. >Physical Technology Engineer, Alcatel CID >[log in to unmask] > >--------------------------------------------------------------------------- ------ >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 >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 >--------------------------------------------------------------------------- ------ ---------------------------------------------------------------------------- ----- 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 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 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 ---------------------------------------------------------------------------------