Thanks for the feedback. I was only trying to correct material property info. The rest of the comments were very relevant. Best regards, Leo Leo M. Higgins III, Ph.D. Sr. Vice President, Engg and Technology ASAT, Inc. 13809 Research Blvd., Suite 635 Austin, Texas 78750 office phone 512-249-4758 mobile 512-423-2002 [log in to unmask] www.asat.com -----Original Message----- From: Stadem, Richard D. [mailto:[log in to unmask]] Sent: Thursday, October 11, 2007 4:46 PM To: TechNet E-Mail Forum; Leo Higgins Subject: RE: [TN] Shielding for BGA rework You're probably right, Leo. I should have clarified. You can place a thermocouple on a PWB and mechanically fasten it. Run it through any oven. Repeat but place a 1/2" long piece of Kapton tape over it. The difference is always 1 degree C less. If I repeat this but use the thermal masking tape (crepe tape) the difference is always -10 deg. C. So the polyimide tape works well for profiling circuit boards, but not the masking tape. The polyimide tape does not work well for sheilding components from rework, but the masking tape does. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Leo Higgins Sent: Thursday, October 11, 2007 4:34 PM To: [log in to unmask] Subject: Re: [TN] Shielding for BGA rework Some comments on the properties of Kapton. Kapton is polyimide. The most widely known polyamide is Nylon. Both are poor thermal conductors. Normal Kapton films have a thermal conductivity of about 0.12 and even Dupont's "thermally conductive" Kapton MT only has a thermal conductivity of 0.37 w/mK. As a reference the thermal conductivities of copper and FR4 are about 400 and ~0.25 - 0.35 (depending upon glass / resin ratio). Best regards, Leo Leo M. Higgins III, Ph.D. Sr. Vice President, Engg and Technology ASAT, Inc. 13809 Research Blvd., Suite 635 Austin, Texas 78750 office phone 512-249-4758 mobile 512-423-2002 [log in to unmask] www.asat.com -----Original Message----- From: TechNet [ mailto:[log in to unmask]]On Behalf Of Stadem, Richard D. Sent: Thursday, October 11, 2007 2:35 PM To: [log in to unmask] Subject: Re: [TN] Shielding for BGA rework Finally, something I know a little bit about. I have learned that Kapton tape should never be used as a masking tape on circuit boards for rework, or for any other purpose either. What I did not know is that Kapton (polyamide) tape generates a gigantic ESD charge (greater than 5kv) when pulled off of the reel, and about 500v when pulled off of the circuit board. This was shown to me by an ESD engineer. I also know that polyamide tape is an excellent heat conductor (not insulator) and does not work very well as a maskant to form a barrier to protect adjacent or surrounding components when performing hot gas rework. It does work well to hold a thermocouple to the board, and the actual temperature drop through the polyamide tape is exactly 1 degree C., so it is OK to use for that, but only on a bare PWB or a scrap board. After the display by the ESD consultant, I now cringe when I go into factories and see the polyamide tape on workbenches. I know there are dispensers that supposedly remove the charge, but how about when the tape is removed from the board? There are masking tapes made just for shielding of other components when doing rework. They look just like the masking tape you use when painting, except they are high-temperature tape and are dissipative. Two companies that make them are Intertape Corp. and 3M. Intertape's p.n. is T-33-1 PRT054. I do not have the 3M tape part number, but I am sure your local 3m rep would be glad to take you out to lunch and give you that info and a whole bunch more. These tapes do have a higher adhesive content and can leave some residue on the components, but an alcohol brushing cleans it off completely. -----Original Message----- From: TechNet [ mailto:[log in to unmask]] On Behalf Of Genny Gibbard Sent: Thursday, October 11, 2007 2:06 PM To: [log in to unmask] Subject: [TN] Shielding for BGA rework Hello again, Does anyone use any shielding for adjacent components and PCB material when they are reworking a BGA, in order to minimize the heat seen by those areas in close proximity? If so, what do you use? Is there a commercially available product, or do you just make your own as needed (someone here said they had seen foil and kapton tape used elsewhere). Thanks much, as always. Genny. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------