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Cu dissolution PTH

Hi All, we are running a process where we are wave solderi... - Jul 05, 2005 by

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Inds

#35294

Cu dissolution PTH | 5 July, 2005

Hi All, we are running a process where we are wave soldering the PTH components using SAC305 alloy. During rework process (using SAC alloy in the solder pot) we are seeing good amount of Cu dissolution, to an extent that the Cu has completely disappeared.. Has anyone come about something like this ? Any Solutions to minimize Cu dissolution in SAC alloy. Will a change of alloy to SN100C do any good.

Thanks inds

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#35296

Cu dissolution PTH | 5 July, 2005

Inds,

This will happen with all lead-free alloys having a tin content above 70%. It takes about 30 sec. for a molten lead-free alloy to totally dissolve a copper pad. The higher the temperature the shorter the time and visa versa. The scary part of this is that the migration or dissolution is also happening at ambient temperatures, except it will take years instead of seconds. A nickel plating is the only solution to stop this migration, but the trade off will be nickel is more difficult to solder. I'm curious what all the lead-free "experts" have to say about this.

You can find more on the subject of copper dissolution here: http://www.smtinfo.net/forum/index.php?showtopic=84 http://www.smtnet.com/Forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=8635&#Message34089

Pat

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#35308

Cu dissolution PTH | 5 July, 2005

We agree with Pat, but it's far from straight forward. [er maybe we should say we don't understand it.]

We duplicated the results of a posting on the web. Flux, then dunk copper wire into tinning pots set at 250*C for measured periods of time. Then measure the reduction in area. Here's what we found: * Many high-tin solders dissolve copper faster than Sn63. * SN100C dissolves copper much slower than the other lead free alloys and even slower than Sn63. * SN100C dissolved the copper slower than SAC305. * SN100C dissolves copper approximately 4 times slower than SAC305 and 2 times slower than SN63 at 250*C.

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Inds

#35331

Cu dissolution PTH | 6 July, 2005

thanks guys for the information..

i am trying out with SN100C and hoping that the Cu will dissolute lesser than SAC305.

inds

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#35336

Cu dissolution PTH | 6 July, 2005

Dave,

Great to see you more involved in the lead-free. I assume the tests you have done were in lab environment, would it be possible to explain how you measured the area reduction (loss of weight or reduction of diameter/thickness) and how did you take the tin layer in consideration. The different lead free alloys have different wetting behavior leaving different amounts of solder deposits. My response to the original thread was more oriented towards awareness of the fact that high tin content alloys are aggressive towards other metals without the data to quantify. What I read about the SN100C is that the alloy is Nickel stabilized and that the Ni prevents intermettalic growth (what makes perfect sense to me). The big question is how long the alloy remains balanced in time and what impurity levels have impact on performance.

I hope Inds can update us after 3-6 months of full production.

Thanks

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Inds

#35340

Cu dissolution PTH | 6 July, 2005

the problem with using SAC305 is we have a very small window within which the connnector has to be removed.. otherwise Cu will dissolute. Now this process window is something between 20sec to 30 sec..depending at what temperature you are reworking the unit and the flow in the solder pot.. now since my solder pot temperature is around 270C (coz of thicker board).. i am lookin at a very small process window to remove and replace the connector...with SAC305..

thats where SN100C comes in the picture. Knowing it has Ni in the composition.. it should act as a barrier to minimize the dissolution of Cu..

So moment I have some information on that.. will let you guys know....

Inds

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GS

#35342

Cu dissolution PTH | 6 July, 2005

Very interesting,

any experience with HASL made by SN100C?

Many Tnks.

GS

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#35346

Cu dissolution PTH | 6 July, 2005

Pat

In response to your questions: Q1. How did you measure the area reduction (loss of weight or reduction of diameter/thickness)? A1. We measured the starting and ending diameter. Then calculated the area [assuming symmetry].

Q2. How did you take the tin layer in consideration? A2. We excluded the tin layer [and IMC] from the measurement.

In response to your comment [Great to see you more involved in the lead-free.]: We don't like to waste the money on foolishness, but ... We expect that so many people will be killed [not that we want that to happen] as a result of lead-free in products that they'll rescind the whole thing.

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#35363

Cu dissolution PTH | 7 July, 2005

Thanks for the response Dave This whole lead free joke gives me ulcers Compare the findings in the real world (threads in this forum) with the conclusions from the lead free industry counsel. The SAC305 is announced the "alloy of choice" here's a link to the report: http://www.ipc.org/3.0_Industry/3.5_Councils_Associations/3.5.1_Industry_Assoc/spvc_bro/SVPC_Final_ExecSumm.pdf

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Inds

#35369

Cu dissolution PTH | 7 July, 2005

Yup Pat, even I read that article.. would love to challange them..but can't..

i think the debate on whether to go lead-free or not.will continue ever and ever after.. WE can call it Lord of the Ring-Part 4 created by europeans..

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#35396

Cu dissolution PTH | 8 July, 2005

Hi Inds,

Don�t forget to give us an update in about 3 months so we can all learn something from real life experience. Common sense tells me that the alloy will be out of balance in 3 to 6 months (depending on volume and board/comp.plating) but I can be wrong. You�re the one who can inform us. Pat

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kris

#41179

Cu dissolution PTH | 25 April, 2006

Inds, Guys

Any updates to share on this issue ?

Thx

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AR

#41196

Cu dissolution PTH | 26 April, 2006

We had x-ray and optical microscopy analyses done on transformers dip soldered with Sn/Pb, SN100C3 and SN100C4 alloys using temperatures 400�C ... 450 �C, with dip times of 2..4 seconds. We found that SN100C4 is at least as good as Sn/Pb 62/38 and SN100C3 nearly as good, when it comes to preventing wire diameter diminishing due to copper dissolution.

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#41349

Cu dissolution PTH | 3 May, 2006

Great to see you have found a solution because now it looks like the component manufacturers will take their share of copper to. Look here http://www.smtnet.com/Forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=10308&mc=2

Inds you have an update for us??

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inds

#41775

Cu dissolution PTH | 25 May, 2006

Patrick, we were seeing a good amount of Cu-dissolution with both SAC305 and SN100C.. couldn't figure out.. till our good old vendors told us that the Cu thickness in the barrel were not correct... but anyway have started some new work with SAC305 and trying out ways to remove and replace unit in minimum time..

do you have any info on how to suck solder out after removing the unit on the solder pot..

will keep you all updated..

inds

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#41791

Cu dissolution PTH | 25 May, 2006

Inds,

Thanks for the update You can remove the solder with a desoldering pump Do a search and you will find all the different options. Just to be clear on the cu-dissolution Did I understand correctly that you didn't see a difference between the 2 alloys?

Patrick

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inds

#41792

Cu dissolution PTH | 25 May, 2006

no there is lot of difference between both the alloys.. SN100C works better than SAC305... gives little more time to remove and replace the unit without completely loosing the Cu... but there are customers who still prefer sticking to SAC305... so the struggle is on..

thanks for your input.. inds

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