Did I buy fake Linear Tech. ICs? - Page 1
Forum section: electronics / general

author: qat
author_rank: Contributor
timestamp: February 03, 2022, 03:07:44 pm
content: Got a couple of LT3797s from Aliexpress since they're more or less impossible to get anywhere else.Since I pretty much expected to get fake or non-working ones I ordered from two sellers and got two sets of different looking ICs.(see images)One set has a white text printed on them in poor quality and the other has laser engraved text on it. The underside is also a little different, one looks to have pads with marks from testing pins and the other has slightly scrached pads (maybe they've spent some time in PnP reject-bucket?). Are LT's chips just different sometimes or did I receive dodgy ones?The chips in general have a unique package so I don't see why anyone would put down the effort to fake these over some unobtanium STM32 which would surely be more profitable.If anyone can provide some insight it would be super helpful!Thanks

author: Algoma
author_rank: Frequent Contributor
timestamp: February 03, 2022, 03:42:37 pm
content: The date codes are quite different, likely reclaimed chips that have been refurbished (sanded?) and tested.

author: qat
author_rank: Contributor
timestamp: February 03, 2022, 04:47:04 pm
content: That’s a very probable explanation, it does looks one of them has some sort of grinding marks. Maybe I’ll have a go with a micrometer gauge and see if there’s a difference. The PCB they’re going on has two of them so maybe I’ll mount one of each and hope I potentially only need to replace one. :-)

author: magic
author_rank: Super Contributor
timestamp: February 03, 2022, 09:06:02 pm
content: The printed ones have date codes all over the place, mostly from early 2010s, they are recycled chips in unknown condition, mostly functional.The lasered ones have identical, fairly recent date code and won't work, may give out magic smoke.So says the crystal ballOne thing I don't understand, which one has the scratches on the bottom and which looks like it was sanded?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 03, 2022, 09:18:46 pm
content: Interesting that the one looks sanded, but the plating looks fine, aside from some probe marks? The other looks virgin, aside from some scratching. Or maybe it was hit with an orbital sander, I don't know...The marking is interesting... offhand, I have one chip (an SSOP-20 or so) that is painted white, solid with no defects. I also have a uModule with larger printing but does show similar voids in the fill. Seems like, for a small QFN, the marking should be solid, that the voiding only occurs in wider fills or something. Not sure offhand if they ever laser mark them, but it sure seems like they would do a better job of it than that.Tim

author: thm_w
author_rank: Super Contributor
timestamp: February 03, 2022, 10:29:00 pm
content: Wonder if the probe marks are factory probe testing. But I don't really see anything special about the IC that would require that.Usually there is no need for seller to test salvaged parts, 99% of them work and its a lot of effort. But I would be impressed if they did.https://www.aliexpress.com/item/1005001425166331.htmlhttps://www.aliexpress.com/item/4000164013731.html

author: qat
author_rank: Contributor
timestamp: February 03, 2022, 11:01:14 pm
content: Quote from: magic on February 03, 2022, 09:06:02 pmThey are in the same position. White one to the left on both.

author: qat
author_rank: Contributor
timestamp: February 03, 2022, 11:17:36 pm
content: Quote from: T3sl4co1l on February 03, 2022, 09:18:46 pmI've seen legit QFNs where the plastic looks sanded in the past. I had a look at some components from my bin and I found a LT3630 (DFN, laser marked) with very slight grinding marks and almost identical test marks. The one with white markings in my picture is one of the best from the bunch, others from the same batch have missing parts of some letters.

author: qat
author_rank: Contributor
timestamp: February 03, 2022, 11:22:21 pm
content: Quote from: thm_w on February 03, 2022, 10:29:00 pmYou managed to find the exact two sellers I purchased from.I have other new parts (directly from Linear) that have test marks too. Like you say it would be very impressive if they were tested by the seller... I think it's more likely they had a look at a new genuine part and hired someone with a needle to put dents in all the salvaged parts to make them look more legit.

author: Algoma
author_rank: Frequent Contributor
timestamp: February 03, 2022, 11:47:34 pm
content: Those vendors do list quite a few for sale, with that many, its more likely to be surplus from a production run. Date codes are more likely New (OLD) stock found sitting in a warehouse.

author: thm_w
author_rank: Super Contributor
timestamp: February 04, 2022, 01:55:17 am
content: Quote from: qat on February 03, 2022, 11:22:21 pmAt least we know that first seller is using real photos, of the ICs they have in stock. So, if the photo is of the actual part, you might be able to tell if its genuine or not, if it has the dots.The second seller appears to be using generic photos, not of the part they ship out (easier to file a claim if it doesn't work?).One other thing, the pads of the left side part are larger than the right side part.Does any other IC use this oddball package? Or other vendors?Quote from: Algoma on February 03, 2022, 11:47:34 pmYou can't necessarily trust those numbers, maybe if it said "58 pieces in stock" I would trust it, but if it says "9999", who knows.But yeah, you are probably right.

author: qat
author_rank: Contributor
timestamp: February 04, 2022, 11:26:31 am
content: Quote from: thm_w on February 04, 2022, 01:55:17 amThe first seller is the one who sent me the parts with white text. The second one seems to have copied the photos from here:https://jlcpcb.com/parts/componentSearch?isSearch=true&searchTxt=lt3797and removed the watermark. What's also worth noting is that the first seller sent me parts in a sealed antistatic bag with printed labels, and the second in a normal clear ziplock with sharpie on it.I also noticed the difference in pad size, at first I thought maybe if one was ground down that'd explain it but that's something I'm starting to find harder and harder top believe.I have yet to find any other component with this package.

author: qat
author_rank: Contributor
timestamp: February 04, 2022, 11:27:07 am
content: What's also interesing is that Linear themselves have two variations of the UKG package. The IUKG and EUKG. In the datasheet it says they are different sizes - 7x8mm vs 7x7mm. However the datasheet only has one drawing for the UKG package, and everywhere else they appear to be the exact same package.In Linear's own database they have material declarations for both; and at the top of both documents it says "QFN 7mm X 8mm Exp. Pad" on both.EUKG:https://www.analog.com/media/en/material-declaration/LT3797EUKG%23PBF.PDFIUKG:https://www.analog.com/media/en/material-declaration/LT3797IUKG%23PBF.PDFMaybe the case here is that I got send one set of IUKGs and one set of EUKGs (which have the same physical markings)?I'm going to send Analog/Linear a message about this discrepancy and report back if they respond.

author: tom66
author_rank: Super Contributor
timestamp: February 04, 2022, 11:43:02 am
content: I think it's more likely the 7 x 8mm is a typo. ST Micro is notorious for their typos and weird sayings in the datasheet (I joke at work that they write the documents in English, translate them into French, then back into English)

author: qat
author_rank: Contributor
timestamp: February 04, 2022, 12:09:50 pm
content: Quote from: tom66 on February 04, 2022, 11:43:02 amI think it’s more likely the 7x7mm is a typo in this case which would make sense. By why two different packages that are identical both dimensionally and in material composition?

author: thm_w
author_rank: Super Contributor
timestamp: February 04, 2022, 11:07:23 pm
content: The website has all 52 lead package as 7x8mm. So its a copy-paste error from the 48 lead package (7x7mm).That is funny though, the I and the E packages:- have the same temp rating- have the same marking on the IC- the I package costs 60c moreSo again, I think they screwed up and put the wrong temp rating for "I" package (industrial), which should go up to 150C. This mistake (?) is in a ton of their other datasheets as well.

author: qat
author_rank: Contributor
timestamp: February 16, 2022, 01:01:11 am
content: Update:Just recieved my PCB today and decided to mount the ICs with the white text and they seem to be legit.