Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Ron Lahat

#12289

Shorts on BGA | 15 March, 1999

After rmoving a BGA (plastic)to correct unexplained shorts I installed another BGA using flux only. Checking on an X Ray machine and found two shorts.

can anyone give a good explenation ?

Thanks

Ron

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Justin Medernach

#12290

Re: Shorts on BGA | 15 March, 1999

| After rmoving a BGA (plastic)to correct unexplained shorts | I installed another BGA using flux only. | Checking on an X Ray machine and found two shorts. | | can anyone give a good explenation ? | | Thanks | | Ron | Ron, It could be a number of factors. Most likely, you had damaged mask in between the BGA pad and via on the substrate. You should also look into your print registration. How are the vias segregated from the pads? Are they tented or is there just a dam in between? Another strong likelihood would be the profile. You can run into a number of problems in BGA rework if the profile is incorrect. An inert reflow atmosphere helps as well. Also, what type of flux did you use? Was it paste flux or was it liquid. You need the tactile strength of paste flux to hold the component in place. If you use liquid flux, the component tends to dance around.

Regards, Justin

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Earl Moon

#12291

Re: Shorts on BGA | 15 March, 1999

| | After rmoving a BGA (plastic)to correct unexplained shorts | | I installed another BGA using flux only. | | Checking on an X Ray machine and found two shorts. | | | | can anyone give a good explenation ? | | | | Thanks | | | | Ron | | | Ron, | It could be a number of factors. Most likely, you had damaged mask in between the BGA pad and via on the substrate. You should also look into your print registration. How are the vias segregated from the pads? Are they tented or is there just a dam in between? Another strong likelihood would be the profile. You can run into a number of problems in BGA rework if the profile is incorrect. An inert reflow atmosphere helps as well. Also, what type of flux did you use? Was it paste flux or was it liquid. You need the tactile strength of paste flux to hold the component in place. If you use liquid flux, the component tends to dance around. | | Regards, | Justin | | Justin,

You young "sea dog" - you just solved my SRT rework problem. You set me straight agout liquid vs. paste flux. Damn you're good and I am either the bad or ugly.

I've been doing S/M touch up for hopelessly mis-registered conditions. Still have some getting through when mask meets specifications. I knew something very dynamic was going on, but hadn't gotten to your conclusions yet.

Thanks a bunch,

Earl Moon

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Justin Medernach

#12292

Re: Shorts on BGA | 19 March, 1999

| | | After rmoving a BGA (plastic)to correct unexplained shorts | | | I installed another BGA using flux only. | | | Checking on an X Ray machine and found two shorts. | | | | | | can anyone give a good explenation ? | | | | | | Thanks | | | | | | Ron | | | | | Ron, | | It could be a number of factors. Most likely, you had damaged mask in between the BGA pad and via on the substrate. You should also look into your print registration. How are the vias segregated from the pads? Are they tented or is there just a dam in between? Another strong likelihood would be the profile. You can run into a number of problems in BGA rework if the profile is incorrect. An inert reflow atmosphere helps as well. Also, what type of flux did you use? Was it paste flux or was it liquid. You need the tactile strength of paste flux to hold the component in place. If you use liquid flux, the component tends to dance around. | | | | Regards, | | Justin | | | | | Justin, | | You young "sea dog" - you just solved my SRT rework problem. You set me straight agout liquid vs. paste flux. Damn you're good and I am either the bad or ugly. | | I've been doing S/M touch up for hopelessly mis-registered conditions. Still have some getting through when mask meets specifications. I knew something very dynamic was going on, but hadn't gotten to your conclusions yet. | | Thanks a bunch, | | Earl Moon | No problem, Earl. How's it going? You sound like you're staying busy. I've been locked up for months now but I think I can see the light at the end of the tunnel. It might be the train though. I'm going overseas for a month. Austria and Hungary. It should be pretty cool. I've never been over there. Oh yeah, by the way, you're probably bad AND ugly but don't worry about it. Take care. Keep the starving infomaniacs happy on here!! I'll pop up when I can.

Justin Medernach

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Mike C

#12293

Re: Shorts on BGA | 20 March, 1999

| After rmoving a BGA (plastic)to correct unexplained shorts | I installed another BGA using flux only. | Checking on an X Ray machine and found two shorts. | | can anyone give a good explenation ? | | Thanks | | Ron | Another possibility Via's not pluged,traces not masked, or mask breaking down are the usual culprits. But during a rework profile it is easy to push to much heat to the top of the BGA causing the corners to curl/bend down which will push the solder balls together. Try increasing the bottom preheat(longer dwell) and minimize the top preheat as much as you can. Lots of luck

Mike C

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forrest xie

#12294

Re: Shorts on BGA | 16 June, 1999

| | | we encounter BGA soldering issue. there is always some dry joint or unclear defects after reflow and the board can't pass electrical test, but if we resoldering it through hot air gun, every thing is ok. we use the "dog bone" surface pad ,that is, no via hole in the center . the BGA we are in use is Hermes PH96 BGA (5102809y54) . How do we solve this?

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