Knowledge of all topics related to various lead-free alloys and the related changes in materials and assembly processes are clearly in limbo. Nearly every single day another problem is found with using lead-free alloys or the hotter processes or the different materials and components, including the printed wiring board. This situation that the EU got the industry into has cost billions of dollars in lost hardware, lost production schedules, etc.
For those of you who can afford to, I would encourage you once again to fully qualify your processes and your product before you ever start production. And I would start with the PWB at the fabrication level.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Wednesday, October 11, 2006 7:30 AM
To: [log in to unmask]
Subject: Re: [TN] Contamination questions

Inge,

a few weeks ago, Keith Sweatman explained everything about the SN100C, highly dopped situation. It seems that the SAC is still a Cu eater.

On the other hand, this is my second attempt to find out things about mixing no-Pb alloys and have very few takers. For me this is a sign that the knowledge about this topic is in the limbo.

Even your italians, maybe our colleague Ivanoe will confirm or infirm my understanding, are not sure: "non credo" esistano problemi, chissà nel tempo come si comporterà.

Thanks for the answer,

Ioan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ingemar Hernefjord
(KC/EMW)
Sent: Wednesday, October 11, 2006 2:48 AM
To: [log in to unmask]
Subject: Re: [TN] Contamination questions


Hi Ioan,

As far as I understand from other's experiments, mixing these two alloys  does not cause any problems. Tests have been done with tempcycling and no  severe (note:severe) failures were indicated. E.g. Chat between two members of a forum like TechNet but in italian:

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sul mix sn/pb con leghe lead free esiste della documentazione che riporta anche gli effetti "visivi" (nel senso che l'inquinamento da piombo fa sì che si formino delle zone con una sorta di macchie). Su internet si trova qualcosa, come foto ed articoli (però non so i link. Li ho visti tempo addietro). 

Sul mix di leghe lead free non credo esistano problemi (anche se indubbiamente l'affidabilità generale del giunto sarà compromessa poichè variano i rapporti di lega). Però è indubbiamente il problema più frequente. Basti pensare che chi produce bobine/trasfromatori/etc. e li prestagna, per ragioni di costo usa nel 99% dei casi una lega sn100. Chiaro che poi andandola a risaldare con una lega sac305 si avranno innanzitutto problemi di rifusione per via delle temperature differenti. E comunque poi il giunto sarà uno strano mix e chissà nel tempo come si comporterà... 

Il problema del mix non è un problema da poco. Se abbiamo pochi dati sui processi controllati ne abbiamo meno ancora su quelli misti. Tra qualche anno ne sapremo certamente di più, ma per ora..... incrociamo le dita
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Note that both alloys are doped in order to minimize copper corrosion. Will be interesting to see what the heavy gurus will say, i.e. Mike Fenner and Werner Englemaier. I'm also interested in your topic, but as I said, never heard of any severe problems like what you fear....

Have a nice day, Ioan!

Inge


 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: den 10 oktober 2006 21:57
To: [log in to unmask]
Subject: [TN] Contamination questions

Hi Free/Net,

since nobody answered my question about how important is to have the same alloy (SAC) at both wave and SMT, versus having SAC in SMT and SN100C in wave, I try to get in through the back door.

The question is about SN100C mini wave pot contaminated with SAC305. In the light of the info that SAC eats the copper in the TH, we've decided to keep the SAC305 in the wave (avoid 2 different alloys on the same assembly), but fill the mini-wave with SN100C. Since mini-waving is less controllable, we would avoid eating all the copper if the operator falls asleep.

But what about dropping a bar of SAC into the SN100C pot? What will be the effect on the board? And what about the reworked joints, some SAC will mix with the SN and create weird alloys in the joints? And what about the SAC that will come down from the pins into the pot?

Anybody has a clue?

Many thanks,

Ioan

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