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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Scotty

#11813

Via's in BGA pads | 21 April, 1999

Does anyone have any experience with soldering 50mil pitch BGA's that have a via in the pad, the size is .012 The via will be masked off on the bottom side of the board. Need to know what precautions or problems if any I might encounter. The process is water soluable.

Thanks Scotty

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joe devaney

#11814

Re: Via's in BGA pads | 21 April, 1999

| Does anyone have any experience with soldering 50mil pitch BGA's that have a via in the pad, the size is .012 The via will be masked off on the bottom side of the board. Need to know what precautions or problems if any I might encounter. The process is water soluable. | | | Thanks | Scotty |

\\Scotty, You may run into problems with voids because the flux solvents and such may get trapped in the via hole. During reflow that trapped liquid will outgas through the solder ball or blow out the solder mask plug on the bottom side. If you can leave the via un-plugged you will be better off. If the board is a wave solder board you might need to apply kapton tape after reflow and before wave solder.

Good luck

Joe

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Justin Medernach

#11815

Re: Via's in BGA pads | 21 April, 1999

| Does anyone have any experience with soldering 50mil pitch BGA's that have a via in the pad, the size is .012 The via will be masked off on the bottom side of the board. Need to know what precautions or problems if any I might encounter. The process is water soluable. | | | Thanks | Scotty | Hi Scotty, That's nutty. Advise against that one and really stress that you don't want to build it because you're going to have long term failure issues, a boat load of opens, and a ton of rework. I'm sure you're a contract house and this is something where you're going to have DFM input. there's no reason why you need via-in-pad on a .050" pitch BGA. You're gonna get screwed with a couple of things. First of all, your going to trap OA flux in the via. It's going to eat the crap out of the board because there is no way you're going to be able to get it out of there. It'll pass test, ionic contamination, and fail a few months down the road in the field because the acid will have done some serious damage by then. Second, via in pad works like a drain. You're going to have a ton of opens. I have boards with via in pad with .008" vias on 0402 pads. I have problems with insufficient solder with those guys. At least I can get at them with an iron. With the BGA on there, an open porks you. Which brings me to my last point, rework. You're going to end up with a ton of it because of opens. My advice would be to push back on the customer and tell them about these issues because they're pretty darn serious. Have the boards sent out to be plated over. This should plug the vias and alleviate some of the concerns. If it's bare copper, this should be no problem. If it's HASL, they just have to strip and replate. If it's tin, they can plate over it. This way the customer won't have to scrap the boards and you'll be able to build the product.

Regards, Justin Medernach

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Murray Pulman

#11816

Re: Via's in BGA pads | 21 April, 1999

Hi Scotty

sorry to stir things up but we assemble some seriously high value boards on a contract basis with vias through bga pads.

However, not blind vias, so there are no cleaning issues & we use 6 though stencils to provide a little extra paste to allow for drain.

The vias actualy allow a massive degree of mis alignment on assembly if your carelesss as the drain drags the device square.

Finaly, we have a customer who puts vias in 100% on all pads and you can put these bga's down by hand with your eyes shut! (not recommended during customer QA audits!!.

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Earl Moon

#11817

Re: Via's in BGA pads | 21 April, 1999

| Does anyone have any experience with soldering 50mil pitch BGA's that have a via in the pad, the size is .012 The via will be masked off on the bottom side of the board. Need to know what precautions or problems if any I might encounter. The process is water soluable. | | | Thanks | Scotty | I tested hundreds of possible combinations in 1964 and 5. None worked either as acceptable quality or long term reliability. Cycles to failure analysis yielded massive amounts of data indicating the process is unacceptable.

Did it again recently with micro-vias in pads. Most failures occurred as outgassing and hole wall issues.

You can place vias in any pad and not even see it if you sequentially laminate MLB's. Then you drill, prepare hole walls, electrolessly deposit copper, electroplate copper, and so on.

There are many options to consider to get your cake and (what the hell has cake got to do with it). I've been gone too long. Anyway, why re-invent the wheel. The RF guys just won't give up.

Also, I did the hole thing to do what someone else said. Five years ago, there were no serious placement techniques so I wanted to place and align by hand. The holes seemed ideal. They weren't.

Earl Moon

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Earl Moon

#11818

Re: Via's in BGA pads | 21 April, 1999

| | Does anyone have any experience with soldering 50mil pitch BGA's that have a via in the pad, the size is .012 The via will be masked off on the bottom side of the board. Need to know what precautions or problems if any I might encounter. The process is water soluable. | | | | | | Thanks | | Scotty | | | I tested hundreds of possible combinations in 1964 and 5. None worked either as acceptable quality or long term reliability. Cycles to failure analysis yielded massive amounts of data indicating the process is unacceptable. | | Did it again recently with micro-vias in pads. Most failures occurred as outgassing and hole wall issues. | | You can place vias in any pad and not even see it if you sequentially laminate MLB's. Then you drill, prepare hole walls, electrolessly deposit copper, electroplate copper, and so on. | | There are many options to consider to get your cake and (what the hell has cake got to do with it). I've been gone too long. Anyway, why re-invent the wheel. The RF guys just won't give up. | | Also, I did the hole thing to do what someone else said. Five years ago, there were no serious placement techniques so I wanted to place and align by hand. The holes seemed ideal. They weren't. | | Earl Moon | May I clarify,

Muy mucho cerveza, porque?

My Mexico adventure, with my proposed future X girlfriend, has vanished before my eyes - unless she reconsiders. I'm left devistated and faced with an unreal reality concerning time. Please help me and add but 30 years to the above stupid reply. During those days I was experimenting with Coors and ceramics. Neither were very compatible, but we made both in Golden.

Moonman

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