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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Micro balls on gold fingers

Richard Jackson

#15848

Micro balls on gold fingers | 18 May, 1998

I've tried every thing I can think of. Do you have any Ideas? What I have is micro balls on the gold fingers of panelize boards. These balls only appear on the gold finger. Or at least I can only find them on the gold fingers. What I have tried so far but still have the problem. 1) changed the oven profile all over the place. Changed ramp rates, soak times and temp, reflow times and temp. 2) Baked the boards. 3) Cleaned every thing. 4) A bunch of other stuff as well. No matter what I've tried I can't seem to get rid of these things. I'm seeing about one finger per panel contaminated with a micro ball. Every now and then I will see a larg splash but Can't determin where it came from. Thanks for any help in advance Richard

reply »

D.Lange

#15853

Re: Micro balls on gold fingers | 18 May, 1998

| I've tried every thing I can think of. Do you have any | Ideas? | What I have is micro balls on the gold fingers of | panelize boards. These balls only appear on the gold | finger. Or at least I can only find them on the gold | fingers. | What I have tried so far but still have the problem. | 1) changed the oven profile all over the place. Changed | ramp rates, soak times and temp, reflow times | and temp. | 2) Baked the boards. | 3) Cleaned every thing. | 4) A bunch of other stuff as well. | No matter what I've tried I can't seem to get rid of | these things. I'm seeing about one finger per panel | contaminated with a micro ball. Every now and then I | will see a larg splash but Can't determin where it came | from. | Thanks for any help in advance | Richard Richard, You may be encountering solder paste contamination on the assembly during the printing process. Solder will reflow on tin/lead plated lands therefore invisible. If you are washing the assembly prior to inspection then you are probably washing residual from solder mask. It will then be apparent that the gold fingers are the only place that solder balls can survive process post cleaning. I have encountered this same problem resulting in insufficient cleaning of underside of stencil. Clean underside of stencil regularly and inspect before cleaning (assuming hydrocleaning). If you are using no clean and refigerate it by any chance then ensure it remains closed to ambient humidity while warming to room temp. Condensation on paste will cause "popping" during rapid preheat.

reply »

Steve Gregory

#15849

Re: Micro balls on gold fingers | 18 May, 1998

Howdy Richard, Welcome to the club! I now dub thee a full fledged member of the "Spotty Gold Finger and Bleeding Ulcer Society"...or SGFBUS for short... (GRIN) I know it's not funny to be in that position, but there's so many different places to pick-up those pesky spots that you gotta just sit back and grin once in a while about it or you'll go coo-coo... I think that most of us have been in this business long enough to have had it happen to us at least a few times. Just when you think you figured out where it was coming from and been watching the area like a hawk over the past week, all the while you're patting yourself on the back for being such a genius, Final QA comes to you and says; "You need to come take a look at some boards we have in final QA, they've got spots on the gold fingers..." It's about then you grab your ol' trusty bottle of Maalox and take a healthy swig... Like I said, it could be happening anywhere, but I'll give you one of the more obscure places that I found where it was happening... I worked at a memory company where we used DEK printers. We had all kinds of different boards that had gold fingers, but when I was working there, only a couple of assemblies would seem to have the problem. They were some new Level-2 Pipeline burst Cache modules that we started building. I went through the same drill as you, dinking with the profiles, inspecting the fabs before they hit the floor, marking certain boards and following them thru the process, inspecting them at each step to see if I could learn where it was happening. I think it's one of Murphy's laws that the harder you look for something, the less likely you are to actually see it...at least it would seem that way to me sometimes. Because when I tried to find it, I couldn't. But as soon as I turned my back, here they were again. I finally figured out where it was coming from, and why it was happening only on the L-2 Cache modules. It was happening in the screen printer. The culprit that was causing it was the automatic stencil cleaner in the printer. Dek has the same kind of "butt-wiper" toilet paper roll cleaner that a lot of other printers have, and what was happening was that whenever the stencil cleaner ran out of solvent, or the roll of paper would jam up when it tried to index to a clean area of paper during a cleaning cycle, would cause the solder paste to just be smeared on the bottom of the stencil instead of being removed. The pattern image for the level-2 Cache stencil was positioned differently on the foil than all of our other modules because of the panel shape and size, and the way we going to run it in the rest of the line. It had the gold fingers pointing towards your belly if you were standing in front of the printer with the board inside the printer. So what was happening that when the paste got smeared on the bottom of the stencil because of what I talked about earlier, the first few boards would get a few tiny solder particles on the fingers that were transferring from underside of the stencil...and once they hit reflow, that little, teeny, tiny solder particle liquifies and spreads itself out on the fingers, sticking out like a sore thumb when you look at it. So after I figured out what was happening, I rotated the image in the stencil 90-degrees and did the same for the pick and place programs. VIOLA'!! No more solder spots! That's just ONE place that it can happen...and I know there's a bunch more places, and probably a bunch as well that I don't have a clue about. Maybe this will help you, if it doesn't, I got some extra coupons that I cut out of the Sunday paper this weekend for some Maalox...it's 39-cents off for the quart sized bottles... I'll send ya a few if ya want...(GRIN) -Steve Gregory-

reply »

Steve Gregory

#15855

Re: Micro balls on gold fingers | 18 May, 1998

...Great minds think alike, huh? (GRIN) -Steve Gregory-

reply »

Mike C

#15850

Re: Micro balls on gold fingers | 19 May, 1998

| Howdy Richard, | Welcome to the club! I now dub thee a full fledged member of the "Spotty Gold Finger and Bleeding Ulcer Society"...or SGFBUS for short... (GRIN) | I know it's not funny to be in that position, but there's so many different places to pick-up those pesky spots that you gotta just sit back and grin once in a while about it or you'll go coo-coo... | I think that most of us have been in this business long enough to have had it happen to us at least a few times. | Just when you think you figured out where it was coming from and been watching the area like a hawk over the past week, all the while you're patting yourself on the back for being such a genius, Final QA comes to you and says; "You need to come take a look at some boards we have in final QA, they've got spots on the gold fingers..." It's about then you grab your ol' trusty bottle of Maalox and take a healthy swig... | Like I said, it could be happening anywhere, but I'll give you one of the more obscure places that I found where it was happening... | I worked at a memory company where we used DEK printers. We had all kinds of different boards that had gold fingers, but when I was working there, only a couple of assemblies would seem to have the problem. They were some new Level-2 Pipeline burst Cache modules that we started building. | I went through the same drill as you, dinking with the profiles, inspecting the fabs before they hit the floor, marking certain boards and following them thru the process, inspecting them at each step to see if I could learn where it was happening. | I think it's one of Murphy's laws that the harder you look for something, the less likely you are to actually see it...at least it would seem that way to me sometimes. Because when I tried to find it, I couldn't. But as soon as I turned my back, here they were again. | I finally figured out where it was coming from, and why it was happening only on the L-2 Cache modules. It was happening in the screen printer. The culprit that was causing it was the automatic stencil cleaner in the printer. | Dek has the same kind of "butt-wiper" toilet paper roll cleaner that a lot of other printers have, and what was happening was that whenever the stencil cleaner ran out of solvent, or the roll of paper would jam up when it tried to index to a clean area of paper during a cleaning cycle, would cause the solder paste to just be smeared on the bottom of the stencil instead of being removed. | The pattern image for the level-2 Cache stencil was positioned differently on the foil than all of our other modules because of the panel shape and size, and the way we going to run it in the rest of the line. It had the gold fingers pointing towards your belly if you were standing in front of the printer with the board inside the printer. | So what was happening that when the paste got smeared on the bottom of the stencil because of what I talked about earlier, the first few boards would get a few tiny solder particles on the fingers that were transferring from underside of the stencil...and once they hit reflow, that little, teeny, tiny solder particle liquifies and spreads itself out on the fingers, sticking out like a sore thumb when you look at it. | So after I figured out what was happening, I rotated the image in the stencil 90-degrees and did the same for the pick and place programs. | VIOLA'!! No more solder spots! | That's just ONE place that it can happen...and I know there's a bunch more places, and probably a bunch as well that I don't have a clue about. | Maybe this will help you, if it doesn't, I got some extra coupons that I cut out of the Sunday paper this weekend for some Maalox...it's 39-cents off for the quart sized bottles... | I'll send ya a few if ya want...(GRIN) | -Steve Gregory- We had a similar problem. But whenever the solder came from the screen printer the solder would wet to the gold fingers, with the help of residual flux. But the problem is balls, that I assume are not wetted to the gold fingers but instead are just stuck on them. We had a case where we had Tin/lead plated vias plugged both top and bottom with solder mask, well what happened was pressure would build in the vias and it would blow out with little balls, and sometimes big ones. Look at the vias and see if you notice any balls in them. Just another place to check. Mike C

reply »

Richard Jackson

#15854

Re: Micro balls on gold fingers | 19 May, 1998

| Richard, | You may be encountering solder paste contamination | on the assembly during the printing process. Solder | will reflow on tin/lead plated lands therefore invisible. | If you are washing the assembly prior to inspection | then you are probably washing residual from solder | mask. It will then be apparent that the gold fingers | are the only place that solder balls can survive | process post cleaning. I have encountered this same | problem resulting in insufficient cleaning of underside | of stencil. Clean underside of stencil regularly and | inspect before cleaning (assuming hydrocleaning). If | you are using no clean and refigerate it by any chance | then ensure it remains closed to ambient humidity while | warming to room temp. Condensation on paste will cause | "popping" during rapid preheat. The posibility of paste contamination during the print process was the first thing I checked as I have run into that one many of times. Even went as far as cleaning the stencil after every print still same problem. I am running a no-clean process so the possiblility of getting water vapor into the paste is quite possible but I went off and printed the paste on a piece of pyrex and ran that through the oven and could not find any spots. But I will still look into the paste issue, Because you are correct in that if the paste is opened while still below the dew point temp. then you will most likly get water in it. I also need to profile my glass to see if it is heating up the same as the board ( which I dought ) so I can run a more acurate test that way. Any ways we continue to bang our heads against the wall on this one... Richard

reply »

Richard Jackson

#15851

Re: Micro balls on gold fingers | 19 May, 1998

| We had a similar problem. But whenever the solder came from the screen printer the solder would wet to the gold fingers, with the help of residual flux. But the problem is balls, that I assume are not wetted to the gold fingers but instead are just stuck on them. We had a case where we had Tin/lead plated vias plugged both top and bottom with solder mask, well what happened was pressure would build in the vias and it would blow out with little balls, and sometimes big ones. Look at the vias and see if you notice any balls in them. Just another place to check. | Mike C Mike, I did find this problem on one of our boards from a particular board vendor. They had put solder mask over the vias on both sides of the board. On this board I could find the balls all over the place. Your assumption that the balls are not wetted to the gold is correct. Every now and then I will find a solder splash on the gold finger which can normaly be traced back to the printer or some other place where the paste was smeared on the board. Does any one know how to attach a picture to one of these posts? If it is possible I will attach a picture of what it is I'm seeing. Thanks Richard

reply »

Mike

#15852

Re: Micro balls on gold fingers | 19 May, 1998

| Does any one know how to attach a picture to one of these posts? If it is possible I will attach a picture of what it is I'm seeing. Yea Email Steve Greg, he is always putting wierd Pics in here, but I like em | Thanks | Richard

reply »

Plasma Prior to Conformal Coating

Heller Industries Mark 5获得了 2015年中国SMT远见奖 - 回焊炉领域