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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Steve Gregory

#16174

Why does everyone want to x-ray BGA? | 16 April, 1998

Hello Ya'll, I've got what may be a silly question, but why does it seem so important to everybody that you have x-ray capability if you're thinking about doing BGA? I know what most people will tell me; "Steve, that's a pretty silly question, it's because ya' can't see the solder joints ya' big boomerang!" Is that the only reason? Because if you stop and think about it, we were building boards with hidden solder joints a long time ago on SIMM's (the caps beneath the DRAM's), it never seemed like a big deal back then...and nobody was rushing out to spend $200,000 on a x-ray machine back then either... So what's the real reason? -Steve Gregory-

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Mike C

#16180

Re: Why does everyone want to x-ray BGA? | 16 April, 1998

| Hello Ya'll, | I've got what may be a silly question, but why does it seem so important to everybody that you have x-ray capability if you're thinking about doing BGA? | I know what most people will tell me; "Steve, that's a pretty silly question, it's because ya' can't see the solder joints ya' big boomerang!" | Is that the only reason? Because if you stop and think about it, we were building boards with hidden solder joints a long time ago on SIMM's (the caps beneath the DRAM's), it never seemed like a big deal back then...and nobody was rushing out to spend $200,000 on a x-ray machine back then either... | So what's the real reason? | -Steve Gregory- Its a conspiracy masterminded by the evil x-ray Manufacturers, They planted false Idea�s that BGA�s require X-ray in order to function Correctly. I worked in a factory where we soldered 9K BGA�s per month without an X-Ray machine in site. Being an engineer an X-Ray Machine would be fun to play with (to inspect for voids, placement, shorts and Opens) but, if you have a closed loop process where you can control your paste and reflow process, is not necessary. During the pre-production and DOE phases I have sent boards out for X-Ray to verify my process, but the best X-Ray machine in the world will not identify a cold solder joint. Regards

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Earl Moon

#16179

Re: Why does everyone want to x-ray BGA? | 17 April, 1998

| Hello Ya'll, | I've got what may be a silly question, but why does it seem so important to everybody that you have x-ray capability if you're thinking about doing BGA? | I know what most people will tell me; "Steve, that's a pretty silly question, it's because ya' can't see the solder joints ya' big boomerang!" | Is that the only reason? Because if you stop and think about it, we were building boards with hidden solder joints a long time ago on SIMM's (the caps beneath the DRAM's), it never seemed like a big deal back then...and nobody was rushing out to spend $200,000 on a x-ray machine back then either... | So what's the real reason?

I applaud everyone's positive attitude and approach to the inspection issue (these are issues - not problems as I learned at Ford Motors). Design for manufacturing and process instead of results (as defect) management is supposed to preclude the need for inspection. The real world teaches otherwise and will continue to do so until true concurrent engineering is a reality. Having started with BGA many years before the technology was acceptable, I learned what you cannot see will hurt you - unless everyone involved in effective process management works together to prevent such pain. Concurrence means engineering, component, component engineering, design, solder paste, PCB, equipment, and manufacturing people all working together to prevent defect at the design level. Well, as nice as this sounds, it ain't happening all the time. It did not happen when we placed chip caps under memory chips as SIMMS. Voiding was excessive to the point of failure even before shipment. Many memory suppliers scratched their domes trying to correct customer complaints concerning memory failures because they were either DOA or failed shortly after insertion. Part of the problem was solder joint defect due to excessive voiding. We still spec and buy components with excessive solder termination contamination as dirt, grease, oxidation, and other crud preventing solder wetting. Most of us don't even do wetting balance or PCB solder wetting testing. We still have solder paste and other solder medium suppliers practicing we won't tell you because we know it won't hurt you. This is true whether solder wetting problems or those concerning cleanliness are discussed. Just look at this forum and you will see the same questions asked over and over again about solders, solderability, and solder process management. I do not advocate constant, 100% inspections, or purchasing two hundred thousand dollar machines of any sort. Far from it - I do advocate simple, sample level inspections and testing so design and process improvement is assured. This gets back to SPC and what it is supposed to do. Without some type inspection or test, before customer validation, we cannot improve. Inspections, when used with SPC, provide the mechanism for continuous design and manufacturing process improvement. Therefore, quality improves - constantly. In line, gray scale X-Ray inspections are not always necessary. High resolution, black and white X-Ray often provides much clearer evidence of excessive BGA solder joint voiding, though not in "real time." This type inspection can be provided on the "outside" as there are many non- destructive test labs available to render sample level inspection data that can be used for SPC and CPI. In fact, black and white often is superior to any other type. Again, I abhor attempting inspecting quality into anything as we all know it can't be done. We have come too far for that nonsense. However, we must continue inspection on a sample level basis and take ISO 9000 (as a poor example of a complete quality system) to where it should be - continuous process improvement and total process management. Sincerely, Earl Moon - Proof Of Design | -Steve Gregory-

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Justin Medernach

#16178

Re: Why does everyone want to x-ray BGA? | 17 April, 1998

| Hello Ya'll, | I've got what may be a silly question, but why does it seem so important to everybody that you have x-ray capability if you're thinking about doing BGA? | I know what most people will tell me; "Steve, that's a pretty silly question, it's because ya' can't see the solder joints ya' big boomerang!" | Is that the only reason? Because if you stop and think about it, we were building boards with hidden solder joints a long time ago on SIMM's (the caps beneath the DRAM's), it never seemed like a big deal back then...and nobody was rushing out to spend $200,000 on a x-ray machine back then either... | So what's the real reason? | -Steve Gregory- Hi Steve, I think it's a "feel good" type of inspection. I come from the contract world. I deal with a million different BGA packages. Parts I have experience with range in cost from 10 dollars to $1260. Manufacturers are the big guys all the way down to some mom and pop semiconductor shop who decides to get into SMT packaging. I have seen problems on BGAs where the BGA package itself (die, glop top, FR4 base)is warped prior to any processing. Imagine trying to deal with that one once it hits the glass transition temp!! Someone in my position needs x-ray and yes, even cold solder has a defect signature, contrary to popular belief. It just takes someone who is very familiar with looking at film to find it (and the right land design). Sure, if I'm an OEM mfr., I can qualify a package and a process and build with these things until my hearts content. I would still want an x-ray station for SPC purposes. Our x-ray system costs 52k. It was well worth it when I consider how many consignment kits I see where solderability may be a big problem. Just some things to consider. Best Regards, Justin Medernach

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Michael Allen

#16177

Re: Why does everyone want to x-ray BGA? | 17 April, 1998

X-ray can be helpful in trouble-shooting BGA component failures. Test techs can quickly determine whether or not a BGA has solder bridges. When a bridge is found, this can eliminate hours of trouble-shooting. And when a bridge is not found, the techs are less likely to remove (i.e., scrap) the part as a "shotgun" approach, so we reduce costs directly that way. It's true that the standard SMT assembly process produces very few BGA solder defects -- too few to justify the x-ray equipment cost. However, the BGA rework (remove & replace) process has a far lower yield. And we're forced to use this rework process fairly often because we consume a large number of high-I/O ASICs in BGA packaging, and these ASICs are more prone to component failures than off-the-shelf parts. So we're reworking a large number of BGAs, and we're finding enough solder bridges on the reworked BGAs that the x-ray equipment cost ($32K) has probably been recouped. (Note: our BGA rework process yields are always improving as we optimize our temp. profiles and use different (or modified) rework nozzles. It might be hard to justify the cost of the x-ray system today, based on our current rework process yields. But the x-ray system paid for itself during our learning curve.)

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D.Lange

#16176

Re: Why does everyone want to x-ray BGA? | 17 April, 1998

| Hello Ya'll, | I've got what may be a silly question, but why does it seem so important to everybody that you have x-ray capability if you're thinking about doing BGA? | I know what most people will tell me; "Steve, that's a pretty silly question, it's because ya' can't see the solder joints ya' big boomerang!" | Is that the only reason? Because if you stop and think about it, we were building boards with hidden solder joints a long time ago on SIMM's (the caps beneath the DRAM's), it never seemed like a big deal back then...and nobody was rushing out to spend $200,000 on a x-ray machine back then either... | So what's the real reason? | -Steve Gregory- Beats the hell out of me??? It is refreshing to hear someone (Mike C.) having experienced process control guided by good 'Ol common sense. I have to agree fully! I've had to fill vias with smt adhesive (imposing as pads), install "spacers"(insufficient solder mask between via and land) and you name it! First rule of thumb is get the design right and be able to recognize what is going to happen to the solder ball during reflow. Is it eutectic? Surface tension plays a role here you know! Registration is the least of your problems as BGA's are very forgiving. Is there sufficient mask to prevent via from scavenging it? You could end up with FR4 on FR4...not much fun! Do you have good screen printing tecniques? X-ray is after the fact! That means REWORK! $$$ Sometimes one has to be resourceful and rely on good ol common sense to build a consistant product whatever and however you do it before you spend the bucks on expensive X-ray equipment (could be your Christmas bonus)! Farm out a few for X-ray analysis if you really need a reality check. There are manufacturers that make valuable tools for verifying your process (www.Toplinedummy.com). Success without X-ray is entirely possibe. I have installed FR4 based ecapsulated die warped like a spoon and achieved consistant results...BGA is new technology but old physics. Lead is Lead!

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G.Wenker

#16175

Re: Why does everyone want to x-ray BGA? | 20 April, 1998

| Hello Ya'll, | I've got what may be a silly question, but why does it seem so important to everybody that you have x-ray capability if you're thinking about doing BGA? | I know what most people will tell me; "Steve, that's a pretty silly question, it's because ya' can't see the solder joints ya' big boomerang!" | Is that the only reason? Because if you stop and think about it, we were building boards with hidden solder joints a long time ago on SIMM's (the caps beneath the DRAM's), it never seemed like a big deal back then...and nobody was rushing out to spend $200,000 on a x-ray machine back then either... | So what's the real reason? | -Steve Gregory-

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Mark

#16181

Re: Why does everyone want to x-ray BGA? | 30 June, 1999

| Hello Ya'll, | I've got what may be a silly question, but why does it seem so important to everybody that you have x-ray capability if you're thinking about doing BGA? | I know what most people will tell me; "Steve, that's a pretty silly question, it's because ya' can't see the solder joints ya' big boomerang!" | Is that the only reason? Because if you stop and think about it, we were building boards with hidden solder joints a long time ago on SIMM's (the caps beneath the DRAM's), it never seemed like a big deal back then...and nobody was rushing out to spend $200,000 on a x-ray machine back then either... | So what's the real reason? | -Steve Gregory-

Steve,

First of all I don't disagree with you, but 104 caps perform a power smoothing function not a data signal function.

A PCB will still function despite a few dead cap locations.

It won't function without certain IC lead contacts.

Dead or Alive Functional testing can kill hi-tech IC's faster than bugs on a windshield. Take a standard BGA pattern, rotate it 90 deg., then functional test. You would be wise to stand back and use your nose to know when it's safe.

When a Customer designs in a BGA, which is an economically driven decision to high level integration, and costly, they want to know that it is running on all cylinders.

This is a significant investment, that they should probably not trust to a company that thinks "aay, a joint here, a joint there what's the problem??".

esad

Mark

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Scott Cook

#16182

Re: Why does everyone want to x-ray BGA? | 1 July, 1999

| Steve, | | First of all I don't disagree with you, but 104 caps perform a power smoothing function not a data signal function. | | A PCB will still function despite a few dead cap locations. | | It won't function without certain IC lead contacts. | | Dead or Alive Functional testing can kill hi-tech IC's faster than bugs on a windshield. Take a standard BGA pattern, rotate it 90 deg., then functional test. You would be wise to stand back and use your nose to know when it's safe. | | When a Customer designs in a BGA, which is an economically driven decision to high level integration, and costly, they want to know that it is running on all cylinders. | | This is a significant investment, that they should probably not trust to a company that thinks "aay, a joint here, a joint there what's the problem??". | | esad | | Mark

Oh, c'mon Mark.....Far be it from me to be argumentative (yah, right....I love a good debate), but I gotta take exception with this mindset. So, tell me, Mark.....have you found an X-ray machine which detects / indicates cold joints on a BGA? Using your logic, you are only checking for OPENS! A cold joint will cause "cylinder misfires" as easily as an open in some conditions.

I think Steve's right. We've also been putting down PLCC's for 20 yearsin the industry. Remember the big deal when they first hit? You can't see all the fillets on those pup's either. Who X-Rays PLCC's?

I say use X-Ray to establish your process windows. OUTSOURCE the X-Ray activity. Put together good balls on the BGA's from the vendor, good pad geometries, and a good convection reflow profile. Then you won't end up with a 200K bookshelf after process development. The boys who developed BGA's in the process (Compaq, Mot, IBM, HP) all tell me that their X-Ray machines served one purpose: Establish the process. Period. They turned 'em off afterwards.........

Scott Cook scook@unicam.com, scook@nettally.com, scook@smtnet.com

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