From: Paul M Fly Brad, Yes there is a risk of damaging the part during rework. But suppose you run a board with an expensive ASIC or FPGA on it and there is an open or short under the FPGA? We had this situation recently. The opens (there were four or five) involved some of the parts control signals and not any of the reprogrammable pins. The part simply would not function correctly without those signals, so now we have a choice, scrap the board or take a chance on the rework process. We were in a prototype mode, so we opted to give rework a shot. I guess it all comes down to how do you make the choice between guaranteed failure (scrapping the board) and potential failure (rework)? We took the chance on rework and the gamble paid off, our already super tight budget didn't have to buy any more very expensive parts and the reworked boards are functioning just fine. Did we get lucky this time? Maybe. Do we have some very highly skilled people in the group that did the work? YES! Did we have a lot of science behind the decision to support us? Not really, just an already overstreched budget and the perceived threat that the project as a whole might be seriously impacted by not doing the right thing. Wish I had a better answer, ************************************ Paul Fly Eastman Kodak Company Engineering Technology Center - PEDT 2400 Mt. Read Blvd. Rochester, New York 14650-3007 Phone: (716) 726-5670 Fax: (716) 726-0275 E-mail: [log in to unmask] ************************************ Brad Kendall <[log in to unmask]> on 03/02/2001 09:05:28 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to Brad Kendall <[log in to unmask]> To: [log in to unmask] cc: (bcc: Paul M Fly/243609/EKC) Subject: [TN] Reballing concern I see that Steve is having parts reballed. I never reballed BGA parts, but have heard of a lot of people doing it lately. I have concerns with reballing and would like to see if you guys agree. Now, it is critical that most BGA parts are NOT exposed to air prior to reflow. I have seen some that have been and they popcorn. So we always kept them sealed or in a nitrogen cabinet. So, now you have run a part, determined there is an open or short, but that the chip itself is good. The board may have been built a week ago, may be sent out of house for rework, thus exposed to climate changes. Then heat is put on it in rework. This part probably has moisture in it and may popcorn. Then you reball and put heat on it again! Is the part any good? It has seen a minimum of 3 heat cycles, if it saw heat for backside glue cure or double reflow or wave, then it has seen even more. I understand reballing is done to save expensive parts, but the risk of destroying the part during rework is a major concern. Brad Kendall --- Bob Perkins <[log in to unmask]> wrote: > Hi Steve > > One thing I have noticed is that if you do not have > your voiding under > control you can create bridging. I have seen a > voids large enough to > expanded the ball enough to invade in the space of > the next ball, and if > that ball has a large void also a bridge can occur. > If this is an known > issue then a new paste may be in order. > > I see two issues with your profile that could > possibly be causing a > problem, I don't think all the balls on the BGA are > reflowing at the same > time. I think you can improve this by setting up > your reflow closer to 183 > before spike. There could also be a hot slump issue > also at the beginning or > reflow, I would recommend you try this to get a more > simultaneous reflow. > > 130 160 180 183 240 > 130 160 180 183 240 > > > How you guys doing in Seattle after that shake up? > We felt it up here in Vancouver. > > Bob Perkins > SMT Manufacturing Process / > Automation Technician > Aitmronics-Delta > > > > > -----Original Message----- > From: Stephen R. Gregory [mailto:[log in to unmask]] > Sent: Tuesday, February 27, 2001 1:34 PM > To: [log in to unmask] > Subject: [TN] Heat-sinked BGA Bridging... > > > Hi all! > > This topic is a "moldy-oldie", but I've started to > experience bridges again > with this TI DSP (TMS320C6201GJC200). I've been > doing okay up unil recently. > We build these boards in work orders of around 25 > pieces. > > Our last run we had 7 boards bridged out of 25!! > Sent the boards out to be > reworked. I asked that they be x-rayed before and > after, and to my surprise > after looking at the x-ray images, they were all > bridging in the same > general > area. > > It's a 4-row periphery BGA, and the bridges are > occuring on the inner two > rows, around the center of the part, at the same > side of the part. > > What's funny, is that the vendor we use to rework > the boards for us is > having > difficulty as well. We've been asking him to remove, > re-ball, and re-install > the part, they said they've been having about a 50% > success rate doing > this...they've been getting the bridges too. They > have a nice full-blown SRT > BGA rework station and do this for a living. > > I print 6-mils of paste (square apertures for the > BGA), have a Conceptronic > HVN-70 which I run: > > 150 160 170 180 240 > 150 160 170 180 240 > > 25-in. per min > > We never have had these problems before...it all > started when TI put the > heatsink into the top of the part. I've looked at > our paste print and it's > dead on, placement is dead on too, we verify that > with a Ersascope. > > My question is could there be something wrong with > the part? Warping causes > bridges at the corners, right? Why would it bridge > in the interior rows at > the same general area? > > Thanks in advance! > > -Steve Gregory- > > --------------------------------------------------------------------------- - > ----- > 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 the > following message: SET > Technet NOMAIL > 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 the > following message: SET Technet NOMAIL > 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 > --------------------------------------------------------------------------- ------ __________________________________________________ Do You Yahoo!? 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