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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Jim Hoxie

#16240

Bottom side bridging | 10 April, 1998

We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated

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Justin Medernach

#16241

Re: Bottom side bridging | 10 April, 1998

| We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a | Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated Jim, Extend the length of the trailing land pad, with relation to how the board is inserted into the wave. This will "rob" the excess solder and prevent bridging. Although it does require a respin. I'm not sure how much you want to extend it. I think the magic number is about .050" but I'm sure someone else will respond with the proper number. Regards, Justin Medernach

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Steve Gregory

#16242

Re: Bottom side bridging | 10 April, 1998

| | We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a | | Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated | Jim, | Extend the length of the trailing land pad, with relation to how the board is inserted into the wave. This will "rob" the excess solder and prevent bridging. Although it does require a respin. I'm not sure how much you want to extend it. I think the magic number is about .050" but I'm sure someone else will respond with the proper number. | Regards, | Justin Medernach Jim, Justin makes a good suggestion, but that ain't helping much now huh? That's the way it usually is anyway...EVERYTHING can be fixed by spinning the fab, but that doesn't help us poor guys on the floor having to deal with it...so what's new? There are a couple of different style "solder-theives" out there...ones like Justin talked about, and there's another style which is another pair of pads placed next to the last pads of a IC footprint...again, when we're talking about the last pads, it's the ones that exit the wave last when you're running them in the machine. There may, or may not be enough room to do any of that...I don't know what you board looks like. But you mentioned something in your post that may shed a different light on things. You said that you were having problems with SO14's, 16's, and 20's. I may be reading something into that, but does that mean you're getting bridges on ALL your boards with these IC's? or is it just on certain boards? If it's with all devices, did this just start happening? Have you been able to wave these things before without any problems? If this is something that's just started happening, and you haven't changed anything major (like fluxes or something) in your processes, can I ask when the last time you had an analysis done on your solder pot? If there's any contamination, or an over abundance of certain metals in your pot, that definitely could give you the problems that you're having. Cadmium, Zinc, and Aluminum in trace amounts will increase the solder's surface tension. Gold and Copper will increase the viscosity...all of the above metals will increase the melting point too. I've got just a few more questions, what temperature are you running your pot at? What is your PCB temp just before it hits the wave? How does the bottom of your board look "flux-wise" just before it hits the wave? Is it really dry? How's the specific gravity of you flux? Is it within the vendor specs? Sorry 'bout all the questions, but these are the same ones you should be asking yourself when you run into something like this. That way, you can eliminate all the variables at your end and feel confident when you tell the designers that they have to roll the rev on the fab so you can solder it reliably. I hope this helps... -Steve Gregory-

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Bob Silveri

#16246

Re: Bottom side bridging | 13 April, 1998

| | | | We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a | | | Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated | | Jim, | | Extend the length of the trailing land pad, with relation to how the board is inserted into the wave. This will "rob" the excess solder and prevent bridging. Although it does require a respin. I'm not sure how much you want to extend it. I think the magic number is about .050" but I'm sure someone else will respond with the proper number. | | Regards, | | Justin Medernach | Jim, | Justin makes a good suggestion, but that ain't helping much now huh? That's the way it usually is anyway...EVERYTHING can be fixed by spinning the fab, but that doesn't help us poor guys on the floor having to deal with it...so what's new? | There are a couple of different style "solder-theives" out there...ones like Justin talked about, and there's another style which is another pair of pads placed next to the last pads of a IC footprint...again, when we're talking about the last pads, it's the ones that exit the wave last when you're running them in the machine. There may, or may not be enough room to do any of that...I don't know what you board looks like. | But you mentioned something in your post that may shed a different light on things. You said that you were having problems with SO14's, 16's, and 20's. I may be reading something into that, but does that mean you're getting bridges on ALL your boards with these IC's? or is it just on certain boards? | If it's with all devices, did this just start happening? Have you been able to wave these things before without any problems? If this is something that's just started happening, and you haven't changed anything major (like fluxes or something) in your processes, can I ask when the last time you had an analysis done on your solder pot? | If there's any contamination, or an over abundance of certain metals in your pot, that definitely could give you the problems that you're having. | Cadmium, Zinc, and Aluminum in trace amounts will increase the solder's surface tension. Gold and Copper will increase the viscosity...all of the above metals will increase the melting point too. | I've got just a few more questions, what temperature are you running your pot at? What is your PCB temp just before it hits the wave? How does the bottom of your board look "flux-wise" just before it hits the wave? Is it really dry? How's the specific gravity of you flux? Is it within the vendor specs? | Sorry 'bout all the questions, but these are the same ones you should be asking yourself when you run into something like this. That way, you can eliminate all the variables at your end and feel confident when you tell the designers that they have to roll the rev on the fab so you can solder it reliably. | I hope this helps... | -Steve Gregory-

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Bob Silveri

#16247

Re: Bottom side bridging | 13 April, 1998

| | | | | | | We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a | | | | Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated | | | Jim, | | | Extend the length of the trailing land pad, with relation to how the board is inserted into the wave. This will "rob" the excess solder and prevent bridging. Although it does require a respin. I'm not sure how much you want to extend it. I think the magic number is about .050" but I'm sure someone else will respond with the proper number. | | | Regards, | | | Justin Medernach | | Jim, | | Justin makes a good suggestion, but that ain't helping much now huh? That's the way it usually is anyway...EVERYTHING can be fixed by spinning the fab, but that doesn't help us poor guys on the floor having to deal with it...so what's new? | | There are a couple of different style "solder-theives" out there...ones like Justin talked about, and there's another style which is another pair of pads placed next to the last pads of a IC footprint...again, when we're talking about the last pads, it's the ones that exit the wave last when you're running them in the machine. There may, or may not be enough room to do any of that...I don't know what you board looks like. | | But you mentioned something in your post that may shed a different light on things. You said that you were having problems with SO14's, 16's, and 20's. I may be reading something into that, but does that mean you're getting bridges on ALL your boards with these IC's? or is it just on certain boards? | | If it's with all devices, did this just start happening? Have you been able to wave these things before without any problems? If this is something that's just started happening, and you haven't changed anything major (like fluxes or something) in your processes, can I ask when the last time you had an analysis done on your solder pot? | | If there's any contamination, or an over abundance of certain metals in your pot, that definitely could give you the problems that you're having. | | Cadmium, Zinc, and Aluminum in trace amounts will increase the solder's surface tension. Gold and Copper will increase the viscosity...all of the above metals will increase the melting point too. | | I've got just a few more questions, what temperature are you running your pot at? What is your PCB temp just before it hits the wave? How does the bottom of your board look "flux-wise" just before it hits the wave? Is it really dry? How's the specific gravity of you flux? Is it within the vendor specs? | | Sorry 'bout all the questions, but these are the same ones you should be asking yourself when you run into something like this. That way, you can eliminate all the variables at your end and feel confident when you tell the designers that they have to roll the rev on the fab so you can solder it reliably. | | I hope this helps... | | -Steve Gregory- Jim, Steve has very good question that should be answered before any changes are made. However a simple solution is to reduce the length of the lead. Reducing the pad size is also an option but is more difficult. Bob Silveri

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D. Lange

#16245

Re: Bottom side bridging | 15 April, 1998

| | | | We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a | | | Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated | | Jim, | | Extend the length of the trailing land pad, with relation to how the board is inserted into the wave. This will "rob" the excess solder and prevent bridging. Although it does require a respin. I'm not sure how much you want to extend it. I think the magic number is about .050" but I'm sure someone else will respond with the proper number. | | Regards, | | Justin Medernach | Jim, | Justin makes a good suggestion, but that ain't helping much now huh? That's the way it usually is anyway...EVERYTHING can be fixed by spinning the fab, but that doesn't help us poor guys on the floor having to deal with it...so what's new? | There are a couple of different style "solder-theives" out there...ones like Justin talked about, and there's another style which is another pair of pads placed next to the last pads of a IC footprint...again, when we're talking about the last pads, it's the ones that exit the wave last when you're running them in the machine. There may, or may not be enough room to do any of that...I don't know what you board looks like. | But you mentioned something in your post that may shed a different light on things. You said that you were having problems with SO14's, 16's, and 20's. I may be reading something into that, but does that mean you're getting bridges on ALL your boards with these IC's? or is it just on certain boards? | If it's with all devices, did this just start happening? Have you been able to wave these things before without any problems? If this is something that's just started happening, and you haven't changed anything major (like fluxes or something) in your processes, can I ask when the last time you had an analysis done on your solder pot? | If there's any contamination, or an over abundance of certain metals in your pot, that definitely could give you the problems that you're having. | Cadmium, Zinc, and Aluminum in trace amounts will increase the solder's surface tension. Gold and Copper will increase the viscosity...all of the above metals will increase the melting point too. | I've got just a few more questions, what temperature are you running your pot at? What is your PCB temp just before it hits the wave? How does the bottom of your board look "flux-wise" just before it hits the wave? Is it really dry? How's the specific gravity of you flux? Is it within the vendor specs? | Sorry 'bout all the questions, but these are the same ones you should be asking yourself when you run into something like this. That way, you can eliminate all the variables at your end and feel confident when you tell the designers that they have to roll the rev on the fab so you can solder it reliably. | I hope this helps... | -Steve Gregory- Have you tried running assembly on oblique fixtures (clearence permitting)? There will be no trailing edge! See Fancort. Your cartrige preheaters must be as close to dancer as possible. Insufficient preheat will definately cause bridging.

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D. Lange

#16244

Re: Bottom side bridging | 15 April, 1998

| | | | We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a | | | Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated | | Jim, | | Extend the length of the trailing land pad, with relation to how the board is inserted into the wave. This will "rob" the excess solder and prevent bridging. Although it does require a respin. I'm not sure how much you want to extend it. I think the magic number is about .050" but I'm sure someone else will respond with the proper number. | | Regards, | | Justin Medernach | Jim, | Justin makes a good suggestion, but that ain't helping much now huh? That's the way it usually is anyway...EVERYTHING can be fixed by spinning the fab, but that doesn't help us poor guys on the floor having to deal with it...so what's new? | There are a couple of different style "solder-theives" out there...ones like Justin talked about, and there's another style which is another pair of pads placed next to the last pads of a IC footprint...again, when we're talking about the last pads, it's the ones that exit the wave last when you're running them in the machine. There may, or may not be enough room to do any of that...I don't know what you board looks like. | But you mentioned something in your post that may shed a different light on things. You said that you were having problems with SO14's, 16's, and 20's. I may be reading something into that, but does that mean you're getting bridges on ALL your boards with these IC's? or is it just on certain boards? | If it's with all devices, did this just start happening? Have you been able to wave these things before without any problems? If this is something that's just started happening, and you haven't changed anything major (like fluxes or something) in your processes, can I ask when the last time you had an analysis done on your solder pot? | If there's any contamination, or an over abundance of certain metals in your pot, that definitely could give you the problems that you're having. | Cadmium, Zinc, and Aluminum in trace amounts will increase the solder's surface tension. Gold and Copper will increase the viscosity...all of the above metals will increase the melting point too. | I've got just a few more questions, what temperature are you running your pot at? What is your PCB temp just before it hits the wave? How does the bottom of your board look "flux-wise" just before it hits the wave? Is it really dry? How's the specific gravity of you flux? Is it within the vendor specs? | Sorry 'bout all the questions, but these are the same ones you should be asking yourself when you run into something like this. That way, you can eliminate all the variables at your end and feel confident when you tell the designers that they have to roll the rev on the fab so you can solder it reliably. | I hope this helps... | -Steve Gregory- Have you tried running assembly on oblique fixtures (clearence permitting)? There will be no trailing edge! See Fancort. Your cartrige preheaters must be as close to dancer as possible. Insufficient preheat will definately cause bridging. D. Lange

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D. Lange

#16243

Re: Bottom side bridging | 15 April, 1998

| | | | We are having a bridging problem with SOIC 14,16 and 20 pin devices during flow solder of the bottom side of our boards. This bridging occurs about half way up the lead between the board and the body of the IC. The chip parts are no problem. The flow solder unit is a | | | Techincal Devices MP16.The chip parts are no problem and our setup is not unusual. FR4,63/37,dancer+laminar wave,no clean and no nitrogen. Any suggestions will be appreciated | | Jim, | | Extend the length of the trailing land pad, with relation to how the board is inserted into the wave. This will "rob" the excess solder and prevent bridging. Although it does require a respin. I'm not sure how much you want to extend it. I think the magic number is about .050" but I'm sure someone else will respond with the proper number. | | Regards, | | Justin Medernach | Jim, | Justin makes a good suggestion, but that ain't helping much now huh? That's the way it usually is anyway...EVERYTHING can be fixed by spinning the fab, but that doesn't help us poor guys on the floor having to deal with it...so what's new? | There are a couple of different style "solder-theives" out there...ones like Justin talked about, and there's another style which is another pair of pads placed next to the last pads of a IC footprint...again, when we're talking about the last pads, it's the ones that exit the wave last when you're running them in the machine. There may, or may not be enough room to do any of that...I don't know what you board looks like. | But you mentioned something in your post that may shed a different light on things. You said that you were having problems with SO14's, 16's, and 20's. I may be reading something into that, but does that mean you're getting bridges on ALL your boards with these IC's? or is it just on certain boards? | If it's with all devices, did this just start happening? Have you been able to wave these things before without any problems? If this is something that's just started happening, and you haven't changed anything major (like fluxes or something) in your processes, can I ask when the last time you had an analysis done on your solder pot? | If there's any contamination, or an over abundance of certain metals in your pot, that definitely could give you the problems that you're having. | Cadmium, Zinc, and Aluminum in trace amounts will increase the solder's surface tension. Gold and Copper will increase the viscosity...all of the above metals will increase the melting point too. | I've got just a few more questions, what temperature are you running your pot at? What is your PCB temp just before it hits the wave? How does the bottom of your board look "flux-wise" just before it hits the wave? Is it really dry? How's the specific gravity of you flux? Is it within the vendor specs? | Sorry 'bout all the questions, but these are the same ones you should be asking yourself when you run into something like this. That way, you can eliminate all the variables at your end and feel confident when you tell the designers that they have to roll the rev on the fab so you can solder it reliably. | I hope this helps... | -Steve Gregory- Your cartrige preheaters must be as close to dancer as possible. Insufficient preheat will definately cause bridging and is prefered to expensive fixturing. Have you tried running assembly on oblique fixtures (clearence permitting)expensive but gives wider margin for such errors? There will be no trailing edge! See Fancort. D. Lange

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