Hans, these were actually boards from PDQFabs when I used to work for ACME. Interesting thoughts on the root cause, not really sure what was going on except we were probably getting what we were paying for. (But the wear and tear was free.) -----Original Message----- From: Hinners Hans M Civ WRALC/LUGE [mailto:[log in to unmask]] Sent: Monday, March 11, 2002 12:00 PM To: [log in to unmask] Subject: Re: [TN] Flattening a board during assembly Hi Dave, Hey, I used to make stuff for Jabil - and your panels always came out flat, honest. Your example is a Lamination Engineer's dream - I never would have seen a double sided board in lamination - unless it's the UL Cert. panels. Two guesses at your double sided problem - either the circuit design top to bottom gave it an induced twist or the material had some flaw from the manufacturer. Diagonal twist makes me think grain direction, No? Normally, you laminate a nice balanced mlb with a reasonable cooldown cycle and the panels come out flat. It really saves wear and tear on your Quality Engineers that way. Hans AC-130 Gunship Motto: "You can run but you'll only die tired." ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hans M. Hinners Electronics Engineer Warner Robins - Air Logistics Center (WR-ALC/LUGE) 226 Cochran Street Robins AFB GA 31098-1622 mailto:[log in to unmask] Com: (478) 926 - 5224 Fax: (478) 926 - 4911 DSN Prefix: 468 -----Original Message----- From: Dave Pahlas [mailto:[log in to unmask]] Sent: Friday, March 08, 2002 5:14 PM To: [log in to unmask] Subject: Re: [TN] Flattening a board during assembly Sounds like in a past life we were the recipients of boards "not done properly". We had 14"x16" double sided PCBs that would twist pretty bad during first assembly reflow making stencil gasketing at second assembly pretty tough. We ran a sample of unpopulated boards through the reflow oven riding flat on the mesh and the diagonal corners actually curled up. We weren't very knowledgeable on PCB fabrication but thought maybe the internal stresses created in the board shop's flattening process were being released in our reflow oven. We never had this problem with the previous (more expensive) supplier. Hmmmm. The product went EOL before resolution was reached, but ... Enjoy your weekend. -----Original Message----- From: Hinners Hans M Civ WRALC/LUGE [mailto:[log in to unmask]] Sent: Friday, March 08, 2002 11:27 AM To: [log in to unmask] Subject: Re: [TN] Flattening a board during assembly Hey Daan, Here's a generic dewarp I've used in the past. You or preferably the Fab house should have an oven large enough to load the panels or boards. If done properly you won't see re-warp during the assembly process. Dewarp is not a board friendly process and I shudder to consider the longer term reliability issues but it gets them flat when nothing else will. It's usually better to dewarp boards instead of panels because of stress relief that occurs at Route. On the other hand a 2 or 4 up panel cuts your cycle time down considerably. 1. Load warped panels into oven. (Keep stacks reasonable sized: ~500 mils of board stock or less - 6-10 panels depending on thickness) 2. Place several Caul plates (that match or overlap panel size) ~50 pounds of weight & Use Kraft Paper (Sulfur Free) to protect panels 3. Bake at 340+ F for 4-6 hours (Material must be at or slightly above Tg) 4. Cool slowly to room temp. 5. Manually assist (Bend & Twist) the dewarp at Final Inspect. (Great upper body workout on those 200+ board shipments) 6. Inspect Panels on Flatness (Granite) Table. ("Tap" test the 4 corners. If the board's corners don't touch the table you've got more flexing to do.) Hans AC-130 Gunship Motto: "You can run but, you'll only die tired." ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hans M. Hinners Electronics Engineer Warner Robins - Air Logistics Center (WR-ALC/LUGE) 226 Cochran Street Robins AFB GA 31098-1622 mailto:[log in to unmask] Com: (478) 926 - 5224 Fax: (478) 926 - 4911 DSN Prefix: 468 -----Original Message----- From: d. terstegge [mailto:[log in to unmask]] Sent: Thursday, March 07, 2002 11:48 AM To: [log in to unmask] Subject: [TN] Flattening a board during assembly Hi Technetters, We've got a batch of boards here that's really twisted (about 1.5 % when measured according to IPC-TM-650) due to imbalanced design. The customers is not willing to change the design, and we discussed with them the possibility of using a carrier-frame for flattening these boards while they are processed through our SMT-line. My worry is that this results in unacceptable stress in the solder joints as soon as the board is released from the carrier. Fortunately there's no BGA on this board, but it does have a small QFP and some 40 mm long SMT-connectors. It's supposed to be a high-reliability military product. Does anyone have any data on the effects of such internal stresses ? Also other comments are welcome. Best regards. Daan Terstegge SMT Centre Thales Communications Unclassified mail Personal Website: http://www.smtinfo.net ---------------------------------------------------------------------------- ----- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------- ----- ---------------------------------------------------------------------------- ----- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------- ----- ---------------------------------------------------------------------------- ----- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------- ----- ---------------------------------------------------------------------------- ----- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------------