Further to Steve's point on mechanical stresses on the components... The feasibility of the suggestion from your assembly house may depend on where in the process the boards warped. If the bare board was warped when the solder solidified on the components, then straightening the boards without reflowing the solder will place the components under stress. This will be the case even if no external force is applied to the board (ie, even if they are just soaked on a flat surface at 150F).
If the bare boards warped as they cooled after reflow/wave, then it is likely that the solder solidified before the boards warped, causing the components to be under stress as we speak. If this is the case (unlikely), then straightening the boards would actually releive the stress. I haven't been in this business long enough to know how hard on components it would be to reflow them a second time. From a mechanical perspective, the best solution would be to reflow the solder, straighten the boards while the solder is still molten and then hold it straight till the boards cool. You might still need to go through a soak period at 150F before the boards would stay straight. Of coarse, running the components through an oven twice could do much more harm than good, not to mention the difficulty in straightening a board at 400 degrees. As Dennis suggested, be careful. Almost anything you do to these boards will shorten their life. Its just a question of how much, and what is the risk if they fail. Darcy Davis Design Engineer, Dynastream Innovations, Inc. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: July 20, 2004 9:55 AM To: [EMAIL PROTECTED] Subject: Re: [PEDA] Board warpage? In a message dated 2004-07-20 11:46:57 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: > A partner in a manufacturing effort is sending us full populated > boards (ICs and passive components) that are badly warped. We sent > them back and rather than get the boards remade and repopulate them, > they want to heat the boards up (fully populated) for three days at > 150 degrees Fahrenheit in order to straighten them out. These boards > perform an extremely important job and I'm worried about the stress > on both the electrical components and the boards themselves. Should > I allow them to do this or should I demand the boards be remade? > My answer would be, "It depends". 150F is 65C, and most commercial spec electronics components are rated to operate up to 70C, and often rated to survive even hotter when unpowered. If all they want to do is let them sit on a flat surface at 150F for three days, and you've got a reliable test procedure for the boards before they go into a higher-level assembly, and you can spare the extra three days, I'd say quietly thank them for the extra burn-in. If they plan to apply some force to encourage the boards toward flatness, I'd be a lot more concerned, particularly given that trying to bend the boards with the solder already solidified will place some fairly large stresses on component leads, and at that temperature the plastic cases will be somewhat more yielding - possibly transferring the stresses to the internal bond wires. You might get some internal opens that way, but what would really worry me would be the possibily of getting an "almost open", that would later fail under normal usage vibration. There would be a lot of other factors involved, like the potential cost of later field failures, product liability, your future relationship with this manufacturing partner, etc., that only you could evaluate. Steve Hendrix * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
