Funny, Sheila,
(no, I don't mean funny Sheila),in fact we have had one year of quarrel and discussions ourselves about this. Reason: we must store components for many years with respect to reparents coming in up and then, as long as for 20 years (!!). How will a todays processor package, or 400pole connector, or a relay etc, how will they behave when you solder them after 1, 2....many years?
First history: open a Philips radio from the 30s and look at the solderings. They use to be amazingly bright and clean still after so many years, and it's easy to resolder. Then open your much younger Philips TV from the 80s and try to resolder the degraded HT supply pins, the ones that make the wondermachine to die exactly when the movie was as best. These pins have been oxidized and mishandled by heat and tempcycling, and you need to use tough methods to get good solderability. Now, why were the former so fresh? Possibly because you used plenty of solder, had a good and clean copper beneath and used handsoldering. Today's components are far from that! The component suppliers try to find ways to save money, and one way is to use as simple and cheap methods as possible. So, Sheila, we felt indignation when we examined a lot of components with questionable finish. What do you think about a porous and thin Tin layer DIRECTLY on Kovar pins? Looked bright and nice on the reel, b!
!
!
ut the wetting balance test told something different: dewetting. Another example is a SOT from famous NEC. The Tin was so porous and thin and cracky after lead bending, that you got naked Iron and Nickel. After P-P these SOTs could be snapped away with a toothpick. Not to bore you with more details, but as long as the field is free for manipulating, you have to be observant on these matters. We decided therefore to store a lot of components in Nitrogene chambers, or vacuum plastic bags, just to save people from getting soldering problems next year and furhter in the future. IF, I say, if the tin plating, and the underlying barrier are thick enough, homogenous and free from built-in impurities, I think that the very thin oxide that will grow during a year, will not cause special problems. RMA takes that easily. But still, we don't risk anything today, component reels come in every week, nothing is stored. So, Sheila, I wouldn't trust the man who says that one year is OK, it dep!
!
!
ends essentially on what finish your components have. I recommend you not to cast the die, but go the serious way with tough specs and incoming inspection and metalurgy survey and so on. Not so funny a way, but safe.
I'm not a MIL-STD crazy, we use commercial transistors from a few cents each to military and space chips that cost 500 dollars each. Even the cheapest ones have to be solderable...
Sheila, I tried to encourage you, really.
Ingemar Hernefjord
Ericsson Microwave Systems
Technetters --
Hope someone can answer this ... how long will parts plated with tin/lead
remain solderable using regular tin/lead solder & RMA flux? These are
metal parts - copper, brass and aluminum. Brass & aluminum have nickel
underplate. My supplier is telling me 12 months @ normal storage
conditions but my captive shop guy is saying "no way"...who's right?
Thanks!
Sheila Smith
Marconi AES
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