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High temperature solder paste for gold plated MCMs

Tuan Bui

#7687

High temperature solder paste for gold plated MCMs | 26 January, 2000

need help in finding the high temp. solder paste (> 221 degree C) to achieve good wetting and shiny filet. Comments and recommedations are welcome.

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Glenn Robertson

#7688

Re: High temperature solder paste for gold plated MCMs | 26 January, 2000

Tuan -

How about Sn/0.7Cu? It's M.P. is 227 and it's readily available. If the leads are Gold plated you might consider pre-tinning them. If you need a higher temp alloy any of the major solder companies can help - I suggets you start with Indium and Multicore.

Glenn Robertson

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#7689

Re: High temperature solder paste for gold plated MCMs | 26 January, 2000

Tuan: Consider Sn 96.5/Ag 3.5 or Sn10/PB88/Ag02 also.

As Glenn says, you had better get rid of that gold or you will never have a shiney connection. Not that a shiney connection means anything about the quality or reliability of your soldering.

My2�

Dave F

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Tuan Bui

#7690

Re: High temperature solder paste for gold plated MCMs | 27 January, 2000

I've tried Indium NC-SMQ92(96.5Sn 3.5Ag) on these MCMs and achieved only marginal wetting on pads and parts. The good wetting is what I try to achieve, shiny is what my engineers want (Prototype environment). Does pre-cleaning the PWBs in ultrasonic solution prior to stencil help or the oven profile needs to be adusted?.

Thanks for any comments and recommendations.

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Glenn Robertson

#7691

Re: High temperature solder paste for gold plated MCMs | 27 January, 2000

Tuan -

One of the reasons I suggested pre-tinning (aside from the negative effects of Gold on appearance and reliability) is the known slower wetting of Sn/Ag and Sn/Cu alloys as compared to Sn/Pb. If you don't have to be Lead-free, the high Lead alloy suggested by Dave might be worth a try. In any case, pre-tinning will be helpful and possibly essential. I doubt that pre-cleaning will help unless there is some evidence of contamination. Assuming that the parts are clean, your problem is one of basic metallurgy and chemistry. Obviously your profile must be adjusted to the characteristics of the alloy and the flux -your paste supplier should help here. Beyond that, most (or all) of the major solder companies are now working to improve the flux formulas used for the higher melting point Lead-free solders. I suggest you check to see if they have something new for you to try. If you need some additional contact names send me a message. Good luck.

Glenn Robertson

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Paulvannan

#7692

Re: High temperature solder paste for gold plated MCMs | 30 January, 2000

We used Promosol Sn96.5/Ag 3.5 during our initial qualification for similar application. We could not achieve a shiny solder joint. Our changes to Sn95.5/Ag 4.5 does not improve the look. In order to confirm the reliability of the joint, I suggest you to run temperature cycling for 100x. If the result is good, the look does not matter since you are assured of reliability.

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Rick

#7693

Re: High temperature solder paste for gold plated MCMs | 12 April, 2000

Glenn and Paul have hit the nail right on the head. Continue working with your solder vendors. I know that many people have succeeded with what you are trying. And the Pb-Free push is only making things better for you as companies develop just what you are looking for (see hot Pb-Free alloy list at www.pb-free.com). Ping me if you want more.

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