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Rehashing Info About Surface Mount Resistor Size

shrtrnd

Jan 15, 2010
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I mentioned this in a hijacking of somebody's surface mount post a few months ago, and saw several replies, so thought it might be of interest here.
I mentioned that years ago I had been buying specific surface mount resistors, and suddenly started receiving smaller-sized surface mount packages, even though I was ordering exactly the same part number. I said I received a response from the company, but didn't know where I filed it. I found it yesterday, and thought I'd share the details.
The company was Stackpole Electronics, Inc (seielec.com).
The year was 2004 that I experienced the problem. The component was their line of RMC Series-General Purpose Thick Film Chip Resistors.
The response from SEI was that the part number I was ordering was a 'legacy format'. That the part was previously rated at 1/2W, but that 'power ratings were changed in 2002', and that the same part I had been ordering was now rated at 3/4W.
Apparently, the vendor I was buying from took it upon themselves to cross reference the 'legacy' part number to the newer SEI part numbering system, and matching-up the wattage requirement (SEI changed from 1/2 to 3/4W), I suddenly started receiving the smaller-sized surface mount package.
In summary:
Stackpole Electronics, Inc. RMC Series General Purpose Thick Film Chip Resistor wattage values changed in 2002.
The result was that wattage handling capability of each chip physical size was increased, allowing Stackpole to reduce the physical size of their chip package to handle the same wattage.
I suppose, since that change was 16 years ago, it doesn't affect many circuits we run into now; but I wanted to share the story in the event somebody sees this phenomenon in older equipment, and wonders what's going on (like I did).

I thought at the time of my post a few months ago that Stackpole was filling my chip request using the part number I had always previously used, but the problem was actually an over-zealous vendor cross-referencing the new Stackpole numbering system to the old numbering system wattage requirement.
...and so ends this trivia story update.
 

BobK

Jan 5, 2010
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They should have substituted the 3/4 W part in the same dimensions rather than the 1/2 W in smaller dimensions.

Bob
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Yeah, I think the a problem when your vendor starts making decisions about what you want
 
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