Hi, Julien, We're having problems also with BGA's but they're failing at vibration testing. Problem is poor solder joints - very course grain structure and fissuring, causing cracking of joints. Reason is soldering temperature is not being reached for these joints. Regarding your problem: I don't know the rework machines you are using, but (fundemental questions, I know) is it only heating the board area you are re-working, or are you reflowing the entire board? If you only re-working a small area, are you first heat-soaking the board to bring the whole thing up to just below the lowest component-maximum temperature rating, and are you continuing to heat-soak it every half hour or so that you're working on it? Long time, low temperature brings EVERYTHING on the board, inside and outside, up to approximately the same temperature. Short time, high temperature brings only surfaces up to temperature - there is insufficient time for the insides of components to heat up. You should use long times and low temperatures that are just below the lowest maximum temperature rating to give the soldering process a "running start" and minimise thermal stress to the board. After that you ramp up the temperatures and shorten the time to bring the lead/pad interfaces up to soldering temperature without taking the component insides beyond their maximum rating. Finally, introduce a very short time, very high temperature 'spike' to take the whole thing up over the soldering temperature and down again, so the solder joints are formed properly but without overheating the inside of the devices. BGA's, especially ceramic ones, seem to be notorious for having cold joints. I think this is because of the number of joints that are shaded from the heat source by the component body, the large surface area of the component to radiate heat back from the balls, and the possibly low max component temp rating of this or other devices on the board that affect the Convection Reflow profile. There, therefore, isn't a long enough dwell time at a high enough temperature to adequately collapse BGA balls and form a good joint without damaging other components on the board at the same time. But these are just my thoughts. You could try what I'm doing and investigate 'Fatigue Resistant Solders' - there's info on the Net, though not a lot. Try Howard Electronic Industries - which have been developed especially for BGA's. These have a very fine grain structure and lower melting point than the usual 63/37 solder and make a better, more flexible joint that is twice as resistant to cracking as joints made with conventional solder, or so it is claimed. The downside to using it is when the convection reflow process is followed by a wave solder process using conventional solder; the FRS tends to reflow because of its lower melting point, and you get problems with the solder joints that were previously made because of subsequent component movement. Largely, an acceptable result comes from adjusting the CR Profile by trial and error and reaching a compromise setting. I feel much work still needs to be done, or be more widely published, on the soldering of BGA's in relation to other components with low max temp ratings. What do you others out there think? Rgds Pete Duncan Asst Principal Engineer Julien Bouchard <[log in to unmask]>@IPC.ORG> on 03/15/2001 08:12:21 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to Julien Bouchard <[log in to unmask]> Sent by: TechNet <[log in to unmask]> To: [log in to unmask] cc: Subject: [TN] Rework profil for BGA Hi everybody, Two week ago, we got a big problem of BGA that do not work after the rework. Almost all BGA fail after the rework. THe BGA is a 27mm x 27mm standard BGA,. We have two reworks machine, an air-vac DRS24 and air-vac DRS22. The problem only occur on the DRS24, which is the newest machine ! We modify the profil to lower the temperature, but my problem is that when i reach around 215 C in the join of the bga, the top of the bga body is around 235C, which is more than the recommanded temperature for BGA by the manufacturer. The profil we use is like : preheat : 2 min at 60% of the flow and 250 C the join reach around 165 C) soak : 1 min at 50% of the flow and 290 C ( the join reach around 180 C ) ramp : 1.5 min at 60% of the flow and 330 C ( the join reach around 215 C ) The BGA are keep in a dry cabinet to redust moisture Does is seem good ? I not sure of the balance between longer time and lower temperaturer versus shorter time and hotter temperature. Anyone have experience with this. Also, when you mesure the temperature, which ball you use : the inner or the outter ? The inner ball seem to be more hot than the other one. Also, for the people who have air-vac machine DRS22 and DRS24, have you problem of stability with the DRS24, compare to the old DRS22. Thank you. Julien Bouchard Matrox - Process Engineer --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------