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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Immersion Ag

Yannick

#19792

Immersion Ag | 6 May, 2002

Hi,

I would like to know if someone is using a immersion AG for their board and if this plating modify the property of the solder paste? do I need to make changes on my temperature profile?

We want to change from HASL to Immersion AG to mount BGA and uBGA is this a could change or do I must change for something else??

thank you for your help

Yannick

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ianchan

#19794

Immersion Ag | 7 May, 2002

Hi mate,

do you mean : 1) Au = "ENIG" or "immersion Au(gold)"? or 2) Ag as in = "silver"?

If Au is the correct term, no need to make extreme changes in your profile. just keep the profile to within your paste specs of preheat, reflow time and reflow peak temperature.

for BGA the usual reflow temperature is 225 deg-C, confirm if your paste specs allow this setting? else the flux will "burn" off and your solder joints will look like crap. reflow timing is subjective to your paste specs. we use around 60-90 sec reflow timing.

try to use the RTS (ramp to spike) profile, for WS paste. try to use the RSS (ramp soak spike) profile, for NC paste.

all our boards currently are 100% using ENIG (Au) plating. we see no problems.

If you really mean immersion silver(Ag), then we haven't gotten to leadfree processes, yet...think its going to be an interesting thread.

do suggest finding out more about Ag properties such as Ag alloy melting point? etc...and incorporating that melting point into your reflow profile "melting reflow" temperature?

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Yannick

#19795

Immersion Ag | 7 May, 2002

Hi,

I reaaly mean AG (Like silver) we was thinking about going with immersion gold butis a bit more expensive. we use a no-clean paste but in a few year( maybe 1-2) we suppose to change to a lead free.

You said that with Immersion gold we change nothing in your profile, the only spec you check is if the peak temperature of the BGA is the same or around the same as your paste. So I suppose is the same thing with immersion AG.

Thank you for the help

Yannick

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ianchan

#19796

Immersion Ag | 7 May, 2002

Hi mate,

checked with one of our egg-brains in the factory (freakin' workaholic still around at this time of night), he tells me that Ag-based PCB finishings share rather similar reflow temperatures for normal Sn/Pb applications. this means (if he is right) that at 183 deg-C your NC paste should have normal solder fusion to the immersion Ag PCB pads. do know that no matter what, the BGA reflow peak temperature should ideally be 225 deg-C for the profile.

You might run this thru' Dave F, for a second opinion.

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#19847

Immersion Ag | 9 May, 2002

We are converting all our ENIG to imm silver.

CHARACTERISTICS * Nominal thickness of the deposit will be 0.1 to 0.3 microns. * Deposit is flat and uniform * It will withstand multiple heat cycles in assembly, which can be problematic with traditional organic coatings (OSP). * Lead free, cost effective, very flat solderable finish. * Excellent solderability, long life characteristics and surface contact functionality. * Imm silver is compatible with all known [to us] solder resist types and assembly fluxes. LONG-TERM STORAGE OF IMM SILVER Not sure what you consider to be long-term storage, but we believe shelf life to be somewhat less [on the order of 12 months] than HASL and much better than ENIG, given adequate environment (20 to 30 C, 40 to 70% R.H.), remain in a sealed package to eliminate air-born contamination, bla bla bla. HANDLING PRIOR TO PLACEMENT/ASSEMBLY * PWB coated with imm silver must be completely dried prior to packaging and all packaging materials must be sulfur-free. * PWB handling is not as sensitive as it is for the OSP finishes. Some people say it is a good practice to wear gloves to prevent potential soiling of the solder pads with human oils and salts. [This is true. It is good practice to handle boards with gloves, especially if you are NC.] We do not wear gloves when handling imm silver [or any other] boards. All PWB, regardless of surface finish, should only be handled by the edges. * This gloved handling maybe more important for operators at the fabricator than those at the assembler. * Side note to possibly link the storage and handling issues: Most immersion silver finishes have a co-deposited organic anti-tarnish in them. ISSUES WITH IMM SILVER * We worry that we made a mistake selecting this material, because the market has not accepted it well and has largely gone to ENIG. Assemblers complain about ENIG, there is not much information about this stuff, not many assemblers are using it, assemblers complain about bla bla bla [Maybe 99% of ROW are waiting for someone to sign on the dotted line that there is nothing wrong with imm silver, it�s reliable and they'll never have trouble with it. The 1% who are using it have done their homework and aren't relying on someone else telling them it is okay.] * We see no change in our solder pot analysis after 6 months, but on the other hand, this product accounts for maybe LT 5% of the board feet across the wave. * Solvents used for solder paste misprint cleaning do not appear to effect the solderability of the imm silver coating. * Insure that the imm silver PWB is completely dry prior to storage or processing. * Does imm silver eliminate migration issues associated with thick pure silver deposits? * Do samples meet UL-796 silver migration test requirements?

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genny

#19867

Immersion Ag | 10 May, 2002

It seems like the biggest problem with silver is its availability. With only a small number of companies offering it, that affects lead time and price. However, everyone I've heard using it seems to think it is excellent. No one seems to have a good answer for why it hasn't caught on, even though it seems to have fewer problems than ENIG. We haven't tried it ourselves, but I believe I heard on a different forum that Lucent has gone almost exclusively to it.

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ianchan

#19885

Immersion Ag | 12 May, 2002

Hi mates,

since I read about this immersion Ag plated PCB, was wondering if its so damm good, why so few people are using it? and why so long to market its PCBA application-virtues?

feedback from bouncing this question around is Ag is prone to corrosion (anyone can input some valid reasons to this?)and that because of the leadfree solder craze, people have found another boggey-man to lean their shoulders on?...

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Yannick

#19888

Immersion Ag | 13 May, 2002

Hi,

Did someone ever heard about Entek? Last week I was speaking to a board manufacturer and he suggest me this coating. You can have information on http://www.enthone.com. It's suppose to be just like a plating that he put on the pad, so you have the copper(which is flat and then the Entek product) So the flatness of the pad is not spoil. And is "good for environment".

So if you ever heard of this I you would appreciate if you can give me your comment on this or anyone else input is great to.

Bye Yannick

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genny

#19895

Immersion Ag | 13 May, 2002

I think for our company, the reason we have not yet tried it is two fold. One - we are just barely starting to see a need on a new product under design for a flat finish, so currently we don't use any of the really flat finishes available. Two - Silver's shelf life is one of the shorter ones, unless you take a lot of precautions in storage. I've heard 6 months, longer with good storage conditions.

We are leaning toward white tin for when we move to flat finishes.

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#19899

Immersion Ag | 13 May, 2002

Entek is Enthone's OSP [organic solderability protection]. It is widely used in the PCB fabrication business. Imidazole (Via Systems) is good, but is not as widely available. Search the fine SMTnet Archive on: * OSP * Entek CU-56, Entek Plus CU-106 * Organic solderability protection * etc

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#19901

Immersion Ag | 13 May, 2002

Are you refering to MacDermid Sterling Silver finish or immersion silver in general. We have had enquiries about Sterling Silver from a customer and the blurb I have read looks very good (don't most sales literature). Has anyone tried this finish?

One of our main PCB suppliers, who has allegedly trialed SS says that after a couple of reflows the PCB becomes very tarnished. Is this true? Or is it their excuse for not wanting to use this silver variant? ('cos they have one of their own, that they don't have to license)

Any tales/experience of Sterling Silver would be appreciated.

Ian

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Andy Hoggan

#20054

Immersion Ag | 24 May, 2002

Teh amount of silver on an immersion silver board won't effect 62/36/2 tin/lead/silver solder, however if the silver on the board is on the thick side and you have a high trace silver content in a 63/37 tin/lead then with the combination of the two you can get preferential cooling due to the silver creating a tertiary alloying phase. It's not important to reliability, but doesn't look too good on the joint, it looks rough.

Silver migration isn't a realistic issue at least no more so than if using 62/36/2 tin/lead/silver alloy

The main problem with the acceptance of the silver finish systems around is that they are very sensitive to water quality, raw materials used, line construction materials, and bath/solution maintenance. Can be a nightmare to run.

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luvtolean

#20060

Immersion Ag | 24 May, 2002

I have used both immersion silver and immersion gold and found that the immersion silver performed better in reliability studies for BGA's using 63/37 paste.

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jason

#21235

Immersion Ag | 19 August, 2002

Hi Andy, Do u also face tombstoning and cold joints when using Ag immersion pcbs ???

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