EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: joseph nicholas on March 04, 2017, 08:39:14 pm
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Can't TO-220 be milled down on the tab to be used instead? The priced differences between the 2 forms can be significant.
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... Because milling and lead-forming a part is substantially more expensive and risks leaving you with damaged parts?
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And it may not be solderable anyway. I once SMT'd an ST part, which I think was nickel plated. Very difficult to tin.
Tim
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And it may not be solderable anyway. I once SMT'd an ST part, which I think was nickel plated. Very difficult to tin.
Tim
Weeeelll, if you're milling it you can just assault it with some sandpaper while you're at it!
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It does seem that the manufactures of basic TO22O parts just use a different drain pad size and cut the metal center pin off and call it a D2PAK.
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And it may not be solderable anyway. I once SMT'd an ST part, which I think was nickel plated. Very difficult to tin.
Nickel plating is solderable. We solder on nickel surface all the time.
The standard DBC (direct bonded copper) process uses nickel plated thick copper, power devices (drain side down) are soldered on nickel pads.
Nickel is used because it doesn't form brittle IMCs like gold, and it doesn't have strong electron migration like silver.
It is also aluminum wire bondable, the Al-Ni bonds are much more strong than Al-Au bonds after thermal cycles.
Nickel surface with think oxidation is hard to tin, though. You need to sand them. But fresh nickel surface can be easily tinned even in unprotected atmosphere.
I have run across the exact same problem that T3sl4co1l describes with some new TO-220 parts although I do not remember if they were from ST; they were a major manufacturer though. The tab looked nickel plated and was very shiny but also practically impossible to solder; I ended up using sandpaper to remove the finish.
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Hmm, could be. Seems thin, yet pretty hard. Could be consistent with a high-P electroless deposit?
Could definitely be oxidized too.
Bad pic:
(https://www.seventransistorlabs.com/Images/TO-220_Nickel_Plated.jpg)
You can't really tell the color because of the lighting, but in the area where I've scratched through, it looks coppery, and with not much scratching necessary. It did take some pressure to scratch through, otherwise the scraper just skated right across.
Exact part,
http://www.st.com/content/ccc/resource/technical/document/datasheet/07/2c/12/ed/d3/c2/42/99/CD00218149.pdf/files/CD00218149.pdf/jcr:content/translations/en.CD00218149.pdf (http://www.st.com/content/ccc/resource/technical/document/datasheet/07/2c/12/ed/d3/c2/42/99/CD00218149.pdf/files/CD00218149.pdf/jcr:content/translations/en.CD00218149.pdf)
but they don't specify plating (at all, it would seem). A quick search doesn't suggest anyone is doing bare nickel (I saw one hit for IR's packaging: lead-free tin plate, nickel underplate).
Rather a lack of information...
Suffice it to say: it's up to you. If you have the parts, and they solder well -- or not -- that's that. Don't expect to be able to look it up in the datasheet, before ordering parts, or without looking at the parts in hand.
Tim