EEVblog Electronics Community Forum
Electronics => Manufacturing & Assembly => Topic started by: hotdiode on September 18, 2021, 11:57:22 pm
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I only buy parts from Mouser and Digi-Key and have observed for the past few years all Texas Instruments PDIP parts (e.g. 74HCT series) have sort of a dull finish on the pins. If I scratch it with metal it's shiny underneath, so I guess it's some kind of oxide layer.
The parts I buy all work fine though I use dual wipe sockets and don't solder them to the board. I've dug out some old projects from years back and the oxidation (if that's what it is) looks no different than how it looks on the new parts. So whatever it is, it isn't getting worse with time. The old projects still work fine too.
In comparison PDIP packages from any other vendor (NXP, OnSemi, etc.) purchased from Mouser/Digi-Key don't look like this. It's only Texas Instruments.
I'm tempted to say it's not a big deal, but I still don't know what I'm dealing with. Any ideas? Do they just use a different metal for the pins compared to other manufacturers?
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I have seen it too. It is weird. Do not know what it is but just in case i use the eraser to clean the pins before soldering.
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How many years have you been noticing that? I have several 2012 through 2017 PDIPs from them and they are still shiny.
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Some part number options are (SN | NIPDAU) (some even NIPDAUAG) - not sure if this could be it...
Otherwise matte tin is good vs bright tin (tin whisker mitigation) ? There was a big push to get away from any "shiny tin" finishes on parts due to this....
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Pics? I thought that matte appearance was something to do with the manufacturing or plating process of the leads on DIP ICs, power transistors, etc. Seems more common than not.
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Here is a photo of a random IC (desoldered but you get the idea) at the bottom and a brand new TI IC at the top. I bought TI glue logic chips from Digikey in a span of 2-3 last years and each time they came with these "oxidized" looking pins. So it is not an affected single batch, and ICs from other manufacturers come with shiny pins, so it is did not seem related to storage problem at Digikey. The TI datasheets I checked did not have anything mentioned like special coating or anything. It is not that they are just matt, they are dark gray like in the photo.
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Thanks for posting the picture Bud, that's exactly what mine look like.
And PeteH thanks for pointing out the NIPDAU finish, this led me to an definitive answer to this question:
* https://e2e.ti.com/support/logic-group/logic/f/logic-forum/718449/faq-why-do-the-leadframes-look-strongly-oxidized-or-corroded
Short answer: It's totally normal and nothing is wrong, they switched from "non-roughened leadframe" to "single-side roughened leadframe" to have better solder adhesion.
There's a more technical discussion here:
* https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/Application-note-Rough-LeadFrame.pdf
Key point: "The non-Rough Leadframe’s relatively smooth surface has a brighter appearance due to the predominant specular reflection. The Rough Leadframe’s textured surface has a darker appearance due to the increased amount of diffused refection." So it's normal that it isn't shiny anymore.
Apparently this visual difference we are observing has an impact on optical inspection systems. Very interesting!
I didn't think much about it until a customer asked if that was normal, and it got me wondering. :)
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Thanks for the info hotdiode. To me such ICs give odd and unnatural appearance to assembled boards where they are mixed with other ICs. As if somebody pulled TI parts from grandma's's closet.
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Great find, hotdiode! Thanks for sharing the info.
I can imagine the rough surface has a larger area for the solder to adhere to the pin.
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Why they become shiny though if i use the eraser on them?
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Bud, I believe any abrasion on the rough surface would smooth it out and make it shiny again.
In that PDF I linked to above on page 4 of 6 the pin surface normally looks like the rough texture on the right. A pencil eraser or magic eraser or fiberglass pen would reduce the roughness so it looks more like the smooth surface on the left image, and that smoothness is what makes it shiny again.
Though according to TI it's the roughness that improves solderability so maybe we want that, even if it's visually unappealing.