Hi Leo! Thanks for the information! I think I'm starting to feel a little better about things now. Your information is pretty darned accurate! Since my last email, I discovered that there were two different Altera devices on these assemblies. We built two each of 4-different part number assemblies (these are prototypes). We had two different matrix trays of what appeared to be the same part, and were told to use one part on one of the pair of assemblies, and the remaining one on the other. I didn't really investigate what the differences were back when we built them, because they at first glance, looked the same...I thought maybe a different die or something like that. But one is a commercial grade Stratix (EP1S30F780C5) that was made in Korea, and the other is a industrial grade (EP1S30F780I6) that was made in Taiwan. I gathered that information from the part numbers... The pictures that you saw on my web page is the commercial grade device. I took a picture of the industrial grade device and posted it on my page. Go directly to: http://www.stevezeva.homestead.com/files/AlteraNoGap.jpg You can really see the difference. This seems to be the one with the 2-piece lid\stiffener assembly that you described. So I'm starting to breathe a little easier now... I've tried to get a hold of someone at Altera all afternoon, because I just want to make sure that the commercial device didn't popcorn as some have suggested. The devices were sealed with dessicant and a HIC card (which was all blue), and weren't opened until they went down on the board Another thing I noticed between the two devices and the way they went together on the board, is that the industrial device has more of what I call; "Squishy Ball Syndrome". Meaning that the weight of the heatsink and the rest of the metal in the device "Squishes" the balls and reduces the stand-off of the part to less than the commercial part does. My question is; at what point does that reduced stand-off become a reliability issue? At what part weight is it determined that high-temp balls should be used to maintain good stand-off? Kind regards, -Steve Gregory- Senior Process Engineer LaBarge Incorporated Tulsa, Oklahoma (918) 459-2285 (918) 459-2350 FAX Leo Higgins <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 07/27/2005 01:11 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Leo Higgins <[log in to unmask]> To: [log in to unmask]@SMTP@Exchange cc: (bcc: Stephen R Gregory/LABARGE) Subject: Re: [TN] Strange Looking BGA Heatsink Gap... Hi Steve, I will send you the Stratix Pkgg info in a subsequent email. This device is a flip chip BGA and is either the EP2S90 or the EP2S130 device, since these are the only 2 Stratix devices with this pin count. FC-BGAs are commonly assembled with a heat spreader attached to the back of the die, leaving a gap to the surface of the build-up substrate that is the thickness of the FC assembly and the thermal adhesive. This may allow the surface mounting of capacitors under the overhanging "lid". I cannot make out what is between the copper lid and the substrate surface in the photo. It looks like it may be two separate elements, with one on the left and one on the right in the photo. The one on the right may be a FC-capacitor, but I cannot tell if the edge view shows the small solder joints that you would expect. Another common FC-BGA construction is a 2-piece lid-stiffener assembly. When the substrate gets over approx 25-27mm on either or both edges, it is common to adhesively attach a copper stiffener ring around the perimeter of the substrate after FC assembly/underfill, and any possible capacitor surface mount assembly. This reduces package warpage and improves FC assembly reliability. In a subsequent step a thermal interface material is applied to the die back and an adhesive is applied to the top of the stiffener ring. A flat heat spreader lid is then mounted against the die back and the top of the stiffener, and the materials are cured. Sometimes due to substrate size limitations it is possible that the stiffener ring will not have constant width around all edges so as to allow capacitor surface mount. So, if your package is made with the top-hat lid (no stiffener ring), and if the two elements seen between the lid and the substrate are caps, you should be OK. But, if the assembly uses the 2 piece lid (stiffener and heat spreader), then the assembly is in trouble. I am afraid that that is what you have, and the stiffener and lid assembly was poor. It is possible that the stiffener is bound to the substrate and there is an intentional gap between the stiffener and the lid, but I have not seen this before, and this would significantly reduce the thermal performance and stiffening characteristic of the package. And even if this is the case, the 'stiffener' does not appear well attached to the substrate. Good luck. Best regards, Leo Director of Applications Engineering ASAT, Inc. 3755 Capital of Texas Highway, Suite 100 Austin, Texas 78704 ph 512-383-4593 fx 512-383-1590 [log in to unmask] www.asat.com The information contained in this electronic message is CUSTOMER/SUPPLIER PRIVILEGED AND CONFIDENTIAL INFORMATION intended only for the use of the individual or entity named above. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution and copying of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by electronic mail. Thank you. -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen Gregory Sent: Wednesday, July 27, 2005 11:35 AM To: [log in to unmask] Subject: [TN] Strange Looking BGA Heatsink Gap... Hi Everyone! We just finished building 8-assemblies that used a 780-ball Altera Stratix BGA on them. These BGA's have a pretty decent sized copper heatsink in the top. Everything went pretty good. But then I noticed something with the BGA heatsink after we got them all built. In the corners, there seems to be some sort of gap beneath the heatsink and the top of the part that I didn't notice before. Go to: http://www.stevezeva.homestead.com then click on Picture Page 2, then look for "Heatsink Gap". All the BGA's show this in all 4-corners. I don't have any more of these BGA's around that haven't been through reflow, so I can't do a before and after reflow comparison. The Altera package drawing doesn't show this gap either. I'm thinking (hoping) that the parts are made like this, to somehow keep the whole part from warping during reflow because of a CTE mismatch between the substrate and the heatsink...it just looks strange though. Anybody else out there familiar with these devices that can tell me this is normal? (Please tell me this is normal!!) Kind regards, -Steve Gregory- Senior Process Engineer LaBarge Incorporated Tulsa, Oklahoma (918) 459-2285 (918) 459-2350 FAX __________________________________________________________________ This message may contain information that is privileged and confidential to LaBarge, Inc. It is for use only by the individual or entity named above. If you are not the intended recipient, you may not copy, use or deliver this message to anyone. 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