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USING LEAD FREE PARTS WITH LEAD PASTE

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Could anyone tell me what the results would be if I used Lea... - Nov 30, 2005 by

james

#38146

USING LEAD FREE PARTS WITH LEAD PASTE | 30 November, 2005

Could anyone tell me what the results would be if I used Lead Free parts with Lead Paste? Will there be solder joint issues? This is kind of new to me to start implementing the lead free process. Thanks for any comments.

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RDR

#38147

USING LEAD FREE PARTS WITH LEAD PASTE | 30 November, 2005

You will be fine as long as you don't run BGAs this way. I would imagine that you have already been doing this for some time already. You might need to increase peak temp and or time with some of the lead finishes.

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#38150

USING LEAD FREE PARTS WITH LEAD PASTE | 30 November, 2005

What are some concerns to expect with BGA's in this situation?

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RDR

#38151

USING LEAD FREE PARTS WITH LEAD PASTE | 30 November, 2005

I would recommend that you search this site. There has been a LOT of discussion on this.

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Mity-C

#38333

USING LEAD FREE PARTS WITH LEAD PASTE | 9 December, 2005

Good Morning,

One problem of LF BGA's in a leaded process is the temps required to propperly collapse the BGA balls. If the BGA is LF, the alloy of the balls will not reflow until the temp reaches 217-245 C. SN 63/37 reflows at 183 C. If your profile is set up based on the requirements of SN 63, you will not reflow the balls of the BGA. The SN63 may form a connection between the board and the uncollapsed ball but you will now have several intermetallic layers and a possible CTE mismatch. I have talked with a Process engineer from Hughes who ran some tests on this issue with one of thier boards and the BGA failed after 200 thermal cycles. I'm sure the results will vary depending on the specifics of the application but concern is valid.

Just My $.02

Chris

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#38367

USING LEAD FREE PARTS WITH LEAD PASTE | 10 December, 2005

Most of the chip; res & caps are already lead-free or RoHS compliant and you most certainly already solder them in your regular leaded reflow process.

However, there are a few more component packages except from BGA:s that are NOT backwards compatible. I should not say packages but components..? For ex. we have a few SSOP:s and a couple of QFP:s which are RoHS compliant and the manufactory spec. says: Do Not solder them in a leaded process.

I do not know why this is; it sounds ridiculous to me except for the BGA:s, which I fully understand.

/Mika

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Mike

#38368

USING LEAD FREE PARTS WITH LEAD PASTE | 10 December, 2005

How about this scenario:

Need to rework a BGA on a 2 year old board. Originally the board was assembled with Sn63/Pb37 and the BGA has eutectic spheres. Now this package only comes with lead free balls. I believe that the board finish is not ideal/ compatible for lead free reflow. What are my options in reworing this package?

I am thinking that Sn63 paste must be used. Should I create a profile for Sn63 or lead free alloy to melt the balls of BGA as well?

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#38369

USING LEAD FREE PARTS WITH LEAD PASTE | 11 December, 2005

If you are taking off the old BGA then the board finish is not the same as it was orginally. I would want to clean the pads off as much as possible and then use sticky flux with the new BGA. But on the other hand, Aim solder has an article about small amounts of lead concentrating in small areas in otherwise leadfree joints.

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#38372

USING LEAD FREE PARTS WITH LEAD PASTE | 11 December, 2005

Hi,

As far as I know soldering a lead free BGA in a lead process is similar to soldering down some BGA's such as ceramic that had high temp solder balls. Remember back when a lot of BGA's had hi temp solder balls that also did not collapse during reflow.

We run lead free parts on everything we make apart from the BGA's which are starting to change over, and have not had any issues yet. Not sure what the fuss is. You just need to make sure the stencil print is ok.

Regards,

Grant

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Kris

#38390

USING LEAD FREE PARTS WITH LEAD PASTE | 12 December, 2005

Can you share the manaufacturer name or links to the documents that you have with this restrictions ?

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Kris

#38391

USING LEAD FREE PARTS WITH LEAD PASTE | 12 December, 2005

Mika

Can you please share the manaufacturer name or links to the documents that you have with this restrictions ?

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Amol Kane

#38414

USING LEAD FREE PARTS WITH LEAD PASTE | 13 December, 2005

Grant, Have you looked at the microstructure of your lead-free BGAs soldered with leaded paste? how do they look?? the reliability of LF BGAs with leaded solder is extremely poor.

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#38422

USING LEAD FREE PARTS WITH LEAD PASTE | 13 December, 2005

Hi,

No because we don't have the ability to do that, and what is the problem with it? Can you describe what happens and how it's different to soldering a high temp BGA solder ball. My guess is if the solder ball does not melt, then there should be no bad intermetalic issues, as the ball becomes a solid terminal?

I would like more info on this if someone has some good articles, as I just don't understand the theory on what would be the root cause of a problem with this.

Regards,

Grant

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#38471

USING LEAD FREE PARTS WITH LEAD PASTE | 14 December, 2005

Hi,

Yes, I would be interested to know what the nature of the high failure rate is with using lead free BGA parts with a lead process. I had been to a seminar where they said it was ok, but not ok to use a lead BGA in a lead free process.

Regards,

Grant

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#38495

USING LEAD FREE PARTS WITH LEAD PASTE | 15 December, 2005

It should be the other way around. A Pb BGA ball will fully melt in a Pb free process, but a Pb free BGA ball will not fully melt in a Pb process, which means the Pb from the paste on the board will not fully diffuse through the ball. This leads to a Pb rich intermetallic area in the BGA ball close to the PCB, which can be weaker than the rest of the ball. The initial connection and performance may be OK, but if your product goes through thermal cycles, the joint is much weaker. I've heard of failures after only 200 cycles or less, while normal acceptable performance may withstand thousands of thermal cycles.

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Kris

#38499

USING LEAD FREE PARTS WITH LEAD PASTE | 15 December, 2005

can you reference who gave the seminar ? maybe they have the solution

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#38501

More Specifics Needed - USING LEAD FREE PARTS WITH LEAD PASTE | 15 December, 2005

The general consensus is - you can run Pb-Free/RoHS parts in a Sn-Pb process as long as you RUN HOTTER.

I've heard that "running hotter" means greater peak temperatures exceeding 217 / 221 C - common SAC alloy eutectic points.

Anybody know any general guidelines on what "hotter" means when you solder a Pb-Free/RoHS part in a Sn-Pb Process??

Also, anyone know what the common plating alloys are on gullwinged devices like QFP's, SOIC's, etc?

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Ola

#38550

USING LEAD FREE PARTS WITH LEAD PASTE | 16 December, 2005

Mika has a point here. AMD has some RoHS compliant components that are Not backwards compatible, in terms of leaded soldering paste & reflow temperature! They are Not willing to tell You Why! I think it has to do with something like: http://www.webelements.com/webelements/elements/text/Bi/key.html Because of the strength of the solder joint. Am I Right on this? Perhaps others will confirm/or totally disagree on this theory?

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Homer J

#38551

USING LEAD FREE PARTS WITH LEAD PASTE | 16 December, 2005

There are some RoHS BGA:s that are within the "so called" solder joint strength & reliability, that can be solder in a non LF-environment! Certaininly LF-free or RoHS BGA will sometimes work the other way around. (I know about the ball melting point). The only issue is: What is the life time of the component/product?

CCGA:s are the hardest packages to get around. Doh'

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Frank

#38553

USING LEAD FREE PARTS WITH LEAD PASTE | 16 December, 2005

The RoHS legislation says that it possible to have an exception from lead. That means that You are allowed to have Pb in the solder joint! While the component and the pcb must be RoHS compliant! Isn't that fun?

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#38563

USING LEAD FREE PARTS WITH LEAD PASTE | 17 December, 2005

Hi,

What worries me is that a lot of people speak about what they have heard, but there is no firm facts on exactly what the situation is.

I did a seminar on lead free a while ago, and was told that going lead free on the components while running lead solder paste was ok. It was said that the lead balls would not reflow, however this is similar to some BGA packages that have high temp solder balls anyway, and these packages never used to reflow the balls either. The story was that not all BGA packages reflow the ball.

However it was said that it was very bad to use lead parts on a lead free solder paste process, because the lead in the balls and pins on components could reflow in latter parts of the process such as a lead free wave solder. So what would happen is the lead coating on the pins would actually reflow at the lower temp, while most of the lead free joint would not, and you would get a bad joint forming. Even if it did not look like the components reflowed again.

So the advice was to change over to lead free components asap. But not to use lead parts in a lead free process, but the other way was ok.

So if anyone has any specific data on this that shows this is wrong, I would really like to know. I remember when people started working with BGA and everyone had horror stories about them, but when we started using them, they were fantastic, and worked great. We never have a problem with BGA, and don't know what the fuss was all about.

I worry lead free might be similar that no one has any specific data and evidence they absolutely have data on. So it's all hearsay, and it makes it hard to know what information's right.

Regards,

Grant

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Homer J

#38566

USING LEAD FREE PARTS WITH LEAD PASTE | 17 December, 2005

Exactly! Maybe I was not clear in my previous thread but this is what I was talking about. Question: How about the Pb exemptions from the RoHS legislation as mention in a previous posting? /Doh'

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Ola

#38570

USING LEAD FREE PARTS WITH LEAD PASTE | 17 December, 2005

>"What worries me is that a lot of people speak about what they have heard, but there is no firm facts on exactly what the situation is."

I do not understand this reply, because what can we do beside listening & read, unless we sometimes ourself do the investigation, which we usually share to the public (unless it is harmful to our business). In this case we had a phone conversation with AMD and they said that this particular component which is a RoHS compliant SSOP Not are backwards compatible. I know for a fact, that there are more component suppliers that offers RoHS compliant components (TSSOP, TQFP, etc.) which is Not backwards compatible in a leaded paste & reflow environment and they do Not tell you this, unless upon a direct question. Still, as I mentioned in previous posting, what exactly does this depend on and what is it in the component terminals that causes this? /Regards

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#38574

USING LEAD FREE PARTS WITH LEAD PASTE | 17 December, 2005

Hi,

The issue I see is they don't tell you why the component is not back compatible.

We have suppliers telling us all kinds of things right now, and I don't think any of them actually know what's going on. No one seems to have firm research that says one thing or another. It's all just "some guy told me" kind of stuff, and that's a worry.

Without firm absolute data, it's all a guess or rumor, which has a huge chance of being incorrect.

Does anyone know of any credible research that covers this topic specifically?

Regards,

Grant

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Ola

#38575

USING LEAD FREE PARTS WITH LEAD PASTE | 17 December, 2005

I agree with You. We are in many ways in the hands of our suppliers; either it is a machine, components, paste, daily consume etc. etc. I can tell You some horrible cock-and-bull story that our suppliers tell us, especially now when the RoHS is new and unfortunately I bet my pant's on that there are some people who buy this. And why not? If You have a trusted firm that you normally do business with, then it is easy to also buy their way of the truth. I think we must have some sense of humor in all of this, after all, we are just humans? About rumors: I've heard something about bismuth. Could this have something to do in conjunction with Pb, so that the solder joint will be affected? /Thanks

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#38576

USING LEAD FREE PARTS WITH LEAD PASTE | 17 December, 2005

AMD and this is the MPN: Asch, I have for some reason lost it, but I will find it later on, if You still think it is necessary. After that we have read through the latest postings we think this is even more important and it seems that we are not alone on this one. It would be very interesting to know if someone "out there" have a similar experience. /Sincerly

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#38578

USING LEAD FREE PARTS WITH LEAD PASTE | 18 December, 2005

Hi,

Yes, and this is the problem with info from suppliers, and the problem is often companies market heavily against new technologies because they have issues with them, or problems not sorted out yet. Sometimes it's just the sales guys who don't understand a new technology, and talk it down, and pick up on any problem with it.

So you can get really weird stories from suppliers.

If someone has specific studies explaining what problems were seen, and what they were caused by, that would be a big help. If there are issues, there must be a report on it somewhere we can check out. I might try doing some searches on it.

Regards,

Grant

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DannyJ

#38590

USING LEAD FREE PARTS WITH LEAD PASTE | 19 December, 2005

Hi Grant,

Here's one paper I came across for a customer of ours, seems they had heard that pb-free bgas cannot be done in pb paste.

http://www.leadfreemagazine.com/pages/pdf/Clech_APEX2004_Paper-final.pdf

I have another from a swiss lab that did shear tests and cross sections within the paper, and if I find it again, I'll forward. It was an excellent paper, just can't seem to track it down on google again.

Mainly, the concern is on life-cycle or reliability. Most tests done show that there is not a *significant* difference using lead free bgas with lead paste, but there isn't enough in the field to solidify those assumptions. (This is a huge generalization...)

I agree with all the statements, I'm just as much in the dark as the rest of you, but will forward anything I find that may be pertinent.

Dan

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Amol Kane

#38593

More Specifics Needed - USING LEAD FREE PARTS WITH LEAD PASTE | 19 December, 2005

there are no issues with running leaded lead free parts with snpb solder. the problem arises when lead-free BGAs are run with SnPb solder. running hotter (i.e mimicing the SAC reflow profile)merely ensures that the sac solder melts and mixes with the sn pn solder. you still have reliability issues on the account of having lead in the solder joints.

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Chris

#38599

USING LEAD FREE PARTS WITH LEAD PASTE | 19 December, 2005

Here is a study from Motorola. Lead free is full of confusion and contradictions. This report may help.

http://www.freescale.com/files/netcomm/doc/package_info/MPC8250PBFREEPKG.pdf

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DannyJ

#38603

USING LEAD FREE PARTS WITH LEAD PASTE | 20 December, 2005

#38636

USING LEAD FREE PARTS WITH LEAD PASTE | 21 December, 2005

Has any one considered the melting eutectic of the plated part verses the eutectic of the paste it self. Inter metallic solids can form when mixing metals. Thus this causes solder joint reliability. Also a lot of vendors are putting out pure tin products in place of lead tined products or 100% matte tin finishes. The leaded process will wet only to a certain level thus leaving a large amount of pure tin lead going up to the package and this area would be prone to whiskering. Also some one mentioned that lead free component terminations have been around for years. This is true but ROHS has not. Plating processes have changed and metals used and mixtures along with thickness have changed also due to ROHS. Also component materials have changed thus increasing the MSL with can still be effected even in a leaded process if bad enough

Handling procedures have changed also.

So can you actually say when I mix Bi in PB it will turn out a good solid solder joint or if I start mixing the new plating of nickel to gold plating with copper under coating I do not need to pay attention to my process because it is a leaded process? What about Embrittlement and inter metallic bonds.

The vendors tell you that it is an easy drop in because this is a vendor driven market sales type of information but in reality it can bit you big time!

O work as a component engineer and see this all the time coming in from vendors. It makes it hard because a lot of management does not understand that even if you want to exempt ROHS will still hit you below the belt if you just say oh well we are leaded anyway. Your parts will end up driving your reliability issues through the ceiling, along with your failure rates.

Good process analysis and internal training structures help not just BOM scrubbing. It is very complex in order to get your present reliability structure to stay or increase in percentage.

Mike Dolbow www.atotalgps.com

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Mika

#38682

USING LEAD FREE PARTS WITH LEAD PASTE | 25 December, 2005

Hi,

The issue I see is they don't tell you why the component is not back compatible.

We have suppliers telling us all kinds of things right now, and I don't think any of them actually know what's going on. >No one seems to have firm research that says one thing or another. It's all just "some guy told me" kind of stuff, and that's a worry.

>Without firm absolute data, it's all a guess or rumor, which has a huge chance of being incorrect.

>Does anyone know of any credible research that covers this topic specifically?

This qustion is interesting and how about the answer? /

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#38820

USING LEAD FREE PARTS WITH LEAD PASTE | 4 January, 2006

Hi,

That's the main problem. I quickly checked out the motorola document, and thanks for posting that, but the main reason for failure seems to be that the ball is not touching the solder pad. I wonder what kind of ball size tolerance they had on the part they were using? All the balls should be the same size and they should all touch the solder paste on the pads I would have thought.

For some not to touch the solder paste means the ball diameters must be really of poor tolerance.

But what I have been told is lead free BGA's are fine with lead process, as they solder down a bit like a lead-less part. The balls don't melt, but it does not matter, as the solder paste still does and attaches the part.

But I don't understand these reports that show some balls not even touching the paste. I need to read in more detail, but just got back from holiday with bad food poisoning!

Regards,

Grant

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#38832

USING LEAD FREE PARTS WITH LEAD PASTE | 5 January, 2006

Grant I'm gonna have to go ahead and sort of disagree with you there. The studies that I've been reading from various BGA Manufacturers have identified insufficient homogenizing / coalescing of the Sn/Pb Paste with the SnAgCu balls.

Ball not touching solder pad indicates more of a process problem with your placement equipment....but it also sounds like you're implying that a SAC Ball produces more ball diameter variation that a standard lead-bearing one; hence, the problems of balls not touching pads....

As far as "not caring" whether the ball collapses or not, and only counting on the melted Sn/Pb solder paste attaching to the ball....I'm gonna have to go ahead and sorta disagree with that one too... You WANT a BGA to collapse and your paste to coalesce with the sphere...it's not the same a ceramic CGA where you don't care whether the column melts and you're just relying on the attachment of your fillet to the column...the solder balls not collapsing with a SAC Ball is the main failure mode when mechanically stressed, and thermally cycled...

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Rob

#38834

USING LEAD FREE PARTS WITH LEAD PASTE | 5 January, 2006

The larger BGA's can also warp more under higher temperatures which causes ball lift, more noticable towards the edges of the package.

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#38842

USING LEAD FREE PARTS WITH LEAD PASTE | 5 January, 2006

Hi,

What studies? Can you post a link?

I am not sure what the difference is between a ceramic BGA that the high temp solder ball is not expected to collapse, and a lead free solder ball that's run through a lead process and also does not collapse because it's run at a lead temp profile.

I just don't see the difference between high temp solder balls on a ceramic BGA that has been used for years, although not a common package, vs a lead free part used in a lead process with lead temp profile. To me it's just a high temp solder ball.

Also, as the my comments on the previous post, those are not our experience, but from reading the Motorola pdf linked in the above post.

The previous post about BGA warping I am unsure of, as I am talking about lead free BGA running in a lead process with lower temps. I don't think that would cause warping, but I could see a lead BGA in a lead free process warping if the component could not handle the temp, plus then you do get interesting issues with the solder mixing. But that's not the topic of my concern's here, it's the other way around.

Has everyone been thinking through this whole thread that we are talking about running the BGA at higher temp, and trying to collapse the ball? That's not what we have been doing, and we are just running lead free BGA's without any problems, but we have been using the same profile as lead BGA's to do it.

The results have been really good, but I am interested in more details. We are just about to go lead free anyway, so this will be come less an issue, but I really would like to see specific info from someone who has done this also, and can relate personal experience. As we have had no problems at all.

Regards,

Grant

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#38848

USING LEAD FREE PARTS WITH LEAD PASTE | 5 January, 2006

Grant,

The strength of the joint in a CCGA is the column for one...it's more ductile, made out of 90% Pb, and it's meant to compensate for the massive CTE mismatches between the ceramic and the board (ie the columns flex to relieve stress from the expanding and contracting ceramic package)...

I haven't really heard anything about relying on just the solder joint to an unmelted/uncollapsed BGA ball. The fillet formation, solder joint thickness, joint strength, and intermetallic are different between a CCGA and BGA ball...All's I know is that for BGA sphere, the ball MUST collapse to get a reliable solder joint...not my theory...just based on lots of studies and literature which you can easily obtain from SMT Mag or look for in Google..

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RDR

#38853

USING LEAD FREE PARTS WITH LEAD PASTE | 5 January, 2006

The CCGA packages that we install are still a tin/lead alloy and not a SAC alloy. They were 90/10 SN/PB. I beleive that this may be one reason why the difference.

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Mike Dolbow Atotalgps.com

#39241

USING LEAD FREE PARTS WITH LEAD PASTE | 20 January, 2006

From what I have seen some component terminal finished have a problem due to storage also. I have seen pure nickel finished turn black. I have seen silver barring finished have problems too. It all depends on how you chose your process, PCB plating, Component terminal finishes, solder paste and the flux suspension chemistry. Also time to actual flow in a turnkey or not process. What ROHS is doing is making manufacturers take more care in the design and timing of their products. I have seen terrible solder joints and I have seen perfect ones that are stronger then most Pb/Sn solder joints. It is all in the process and design engineering side that makes or breaks this process with ROHS.

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Mike Dolbow Atotalgps.com

#39242

More Specifics Needed - USING LEAD FREE PARTS WITH LEAD PASTE | 20 January, 2006

I have seen 100% Matte Tin plating and a lot of Sn/Ag/Cu plating for gull wing parts. This is the most common type of plating. Also in a lead free process you will see that the very end Toe of the part will not flow. This is due to the metal being cut from stock. It is usually copper inside and it is then exposed on the very end at the cut. During the high heat process of lead free it oxidizes at a much greater rate and thus you do not get good flow or wetting in that area. By the new IPC standards that is ok, not a failure.

As far as hotter well for my general rule I try to reach 5 to 10 Deg with in the actual plating Eutectic. So in most cases my PCB and component terminal plating are with in 5 to 10 deg of each other. This helps also if you match a past chemistry to this. What you get is a more reliable solder end joint and an easier process to engineer. Greater wetting and bond.

Less of induced reliability problems.

Mike A Total Green Planet Solution www.atotalgps.com

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#39434

USING LEAD FREE PARTS WITH LEAD PASTE | 1 February, 2006

See the paper presented by M Simard Normandin at the International Lead free conference in Toronto May 24th 2005

link to the paper is available on our website under the event http://www.muanalysis.com/about/events.html

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#39459

USING LEAD FREE PARTS WITH LEAD PASTE | 1 February, 2006

Hi,

What's the difference between soldering a lead free solder ball BGA onto a footprint with lead solder paste when the ball does not collapse, compared to a lead-less package. The BGA is bigger, but you rely on the solder paste only, seems to work for every other component on the board.

We are doing this on one component on one of our products, and we have not had any issues soldering lead free using lead solder paste. Although we are about to stop when the lines change over to lead free.

But I don't think this is a big problem.

Regards,

Grant

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Cal Kolokoy

#39462

USING LEAD FREE PARTS WITH LEAD PASTE | 1 February, 2006

Your method of only using solder paste to form the solder joint w/out collapsing the ball is very unconventional, just as others have mentioned on this thread.

I bet you those joints will fail under thermal and mechanical stress. Have you done due-dilligence and have these analyzed at a lab? I would. I would not want to be the guy having to answer to future field failures.

Is your end product something that does not see any harsh environments whatsoever?

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