Fake semiconductors  - Page 1
Forum section: electronics / general

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 24, 2020, 03:25:01 pm
content: It's probably been discussed before, but I've purchased a few pnp TIP36c from everyone's favourite auction site. I haven't got any high quality analysing equipment for transistor testing. I have used diode check from bae to emitter, and base to collector and it looks like some real TIP36c transistors I have from a very reputable supplier. Where it doesn't look right is the package. Shorter metal for heat dissipation on the contact surface, flash around the mounting hole. I suppose what I'm wandering, is how good are they if indeed they are fake. I will post a picture of known good transistor and suspect fake package. The other thing is the plating on the contact surface and the legs. It kind of resembles cheap bling jewellery patina. I will get a photo up. And if destructive testing, how to remove the package casing. I haven't got any acid of any kind. I do have dremel cutting wheels.Thanks for reading. Any thoughts appreciated.

author: Haenk
author_rank: Super Contributor
timestamp: April 24, 2020, 03:37:36 pm
content: There are at least 5 manufacturers, plus parts do change in look over the years.Hard to judge without pictures...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 24, 2020, 04:04:55 pm
content: Use heat, and lots of it. A hot air machine on its highest setting (or nearly there), or heat gun, or a low flame until the packaging is noticeably soft and maybe smoking a bit. The plastic will soften and can be removed with pliers. The die is either epoxied or soldered to the tab, so will lift off easily. Getting the die out of the plastic may not be as easy (you need to flex the plastic while hot to peel it away from the die, and break the bond wires), but it's not like you need to inspect the pattern, die area will be important information already. (That said, you may compare pattern to known dies and see if it's some 2N3055 floor sweepings, or a skookum interleaved or perforated emitter, or what.)Runner-up is bashing it edgewise with a hammer. The plastic fractures and the tab bends, delaminating it. Usually the plastic top comes off more or less whole, less whatever crumbled off the sides, and takes some or most of the die with it. Don't expect to see the die pattern this way, but the area will still be apparent.As for (usually) nondestructive testing, simply setting up a circuit to do things is the way to go. Signal generator at low duty cycle, Darlington configuration to get adequate base current available, nice low load resistance, and a power supply of whatever voltage you want to test at and enough capacitance to hold it up during the pulse (if it's not rated continuous). A 1A transistor (say they put 2N4401 dies in the poor things) simply won't sink, say, 10A -- no matter how hard you blast it* -- but a proper power transistor will, easily.*In fact, 10A is pushing it, even under the most intense avalanche conditions. In those subnanosecond pulse generator circuits you might've seen around, the PN2369 (typically, but others work too) tops out at 200mA under normal conditions, but sinks over an ampere in this condition. I don't think there's any way to make a BJT carry any more current than this, aside from turning the whole thing to plasma...Also tells you switching speed, under given drive conditions (e.g., don't forget R_BE to keep turn-off reasonable).Vcbo can be tested simply by wiring C-B as a zener, with a pullup resistor and a ~high voltage supply. Limiting current to say 1mA, few transistors will die under this condition; and if they do, they're probably not worth your time anyway.Tim

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 25, 2020, 12:42:17 am
content: Great tips on destructive testing, I can do heat from a 120 watt gas iron. Couple of pictures, the flash bounced off the bling contact face. The clearest two transistors are what I suspect as fake. Forward voltage drop was 0.715 to 0.720 and was consistent across 35 transistors.

author: wraper
author_rank: Unknown
timestamp: April 25, 2020, 12:58:26 am
content: First 2 are recycled and not from ST, they were completely dipped into solder, not just terminals. Second 2 look genuine but recycled/used.

author: coppice
author_rank: Super Contributor
timestamp: April 25, 2020, 01:03:40 am
content: My guess is they are real TIP36Cs made by ST, but they are second hand ones that have been scavenged from old equipment. The legs are obviously not fresh from the factory. The visual differences in the package are typical of what you see between batches. If one batch goes to assembly an test house A, and another goes to assembly and test house B there can be significant visual differences between parts ordered at the same time. Add in the differences they make to packages over time, and the visual differences may be even greater for devices made several years apart.

author: wraper
author_rank: Unknown
timestamp: April 25, 2020, 01:06:14 am
content: Quote from: coppice on April 25, 2020, 01:03:40 amThey are not. It's not original ST marking and lead frame is different.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2020, 05:58:10 am
content: Quote from: wraper on April 25, 2020, 12:58:26 amOh yeah, top two in 2nd pic, are the tabs not even flat? I think I can see just a little wobble in there. Might just be what's reflecting, of course.Which are the left two in 1st pic, which look better printed. They might actually be authentic, but yeah, recycled likely. Printing on the other pair looks poor, but that may just be lighting, or contamination (fingerprints for example soak into the lettering, making it hard to read; try wiping with acetone?). I don't have any ST TIPs to compare, personally.But in any case, noteworthy that we've collectively spenttwo orders of magnitudemore labor in discussing the subject, than simply buying the right parts in the first place.If in doubt, yes, it's shite.Tim

author: coppice
author_rank: Super Contributor
timestamp: April 25, 2020, 11:44:49 am
content: Quote from: T3sl4co1l on April 25, 2020, 05:58:10 amYou make it sound easy to obtain the right parts. With various levels of fakeness getting all over the supply chain it can be really tough, unless you can go to the primary source. Thankfully, the increasing amount of things which can be ordered directly from the original vendor's web site is making this easier for small users. Hopefully this type of access will become universal over time.

author: coppice
author_rank: Super Contributor
timestamp: April 25, 2020, 11:47:57 am
content: Quote from: wraper on April 25, 2020, 01:06:14 amI'm not familiar with ST's marking scheme, but are you sure you are familiar with every variant of lead frame ST have used over 4 decades of making TIP36C clones?

author: wraper
author_rank: Unknown
timestamp: April 25, 2020, 12:26:40 pm
content: Quote from: coppice on April 25, 2020, 11:47:57 amTO-247 variant is made only since 2008. Font used in marking is wrong. Also in datasheet there is only one variant of lead frame/package shown. Page 7https://www.st.com/resource/en/datasheet/tip36c.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2020, 12:53:48 pm
content: Quote from: coppice on April 25, 2020, 11:44:49 amIn a non-production context, it's far cheaper to get 95%+ confidence from mainstream distributors versus <5% confidence from eBay or Ali.In production, that last 5% is worth a lot, maybe even worth doing qualifications on cheaper sources with lower confidence, but not here.Tim

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 25, 2020, 02:20:03 pm
content: Thanks for the replys, the two in transistors to the right are the real thing. The poorer labeling on them is from me handling them I think etc. The contact surface of the first two transistors is, or seems perfectly flat. If they function as good as good as the two on the right, I'm ok with that. I can understand production processes changes over years or even decades. So may not look the same. It was just the bling metal look, and slightly scruffy looking, and the plastic flash on a few of them. Another notable observation was a few had holes where the plastic didn't look quite concentric, it's ever so slight and not on all of them. I will find out in use if they can deliver on the money and under load conditions.

author: magic
author_rank: Super Contributor
timestamp: April 25, 2020, 06:22:02 pm
content: Quote from: T3sl4co1l on April 24, 2020, 04:04:55 pmBending the plastic while hot is one way (seems a bit risky to the die), another is to keep it hot and smoking for several minutes - the plastic decomposes and becomes brittle like charcoal. Repeat if some of it is still too hard inside.