Also the heatsink's mass will stress the solder joints if they are not mounted to the PCB...But the biggest problem I have seen is that the heat sink hits things in transport and handling...I have also seen people use the heatsinks used as handles on PCAs... The other possibility is that the BGA balls may have an adhesion problem with the BGA substrate... This should be observable when the BGA is removed. Paul Paul Edwards Surface Art Engineering -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner engelmaier Sent: Thursday, December 04, 2008 8:14 PM To: [log in to unmask] Subject: Re: [TN] 答复: Re: [TN] BGA soldering open issue Nee hao Hechong, BGAs with heatsinks have been shown to warp and thus loading the SJs in tension. Werner -----Original Message----- From: Cong He <[log in to unmask]> To: [log in to unmask] Sent: Thu, 4 Dec 2008 10:08 pm Subject: [TN] 答复: Re: [TN] BGA soldering open issue surface finish is hasl. after analysed parts of the board, we found some balls of the bga rupture. Could it be the material of the ball(BGA) cause the problem? by the way, there is a heatsink which is double size lager than the chip stick on it without other fixture. will the heatsink be the reason? Hechong "Wenger, George M." <[log in to unmask]> 发件人: TechNet <[log in to unmask]> 2008-12-05 10:57 请答复 给 TechNet E-Mail Forum <[log in to unmask]>; 请答复 给 "Wenger, George M." <[log in to unmask]> 收件人 [log in to unmask] 抄送 主题 Re: [TN] BGA soldering open issue What is the surface finish on your PCBA? Necong, What is the surface finish on your PCBA? Regards, George George M. Wenger Andrew Wireless Solutions Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [Office] (732) 309-8964 [Cell] [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Cong He Sent: Thursday, December 04, 2008 9:09 PM To: [log in to unmask] Subject: [TN] BGA soldering ope n issue dear all: I am facing a problem of bga soldering. when the board have just soldered ,it pass all test. But after sometime, maybe for a few weeks, some of the bga balls opened. the function became normal if i press the chip on the top side. It seems that the pcb didn't warp much,it seems even no warp at all. Does any of you know why? And how to improve? 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