What secret lies under that blob? - Page 1
Forum section: electronics / beginners

author: Merlysys
author_rank: Regular Contributor
timestamp: January 20, 2014, 02:28:25 pm
content: I often come across chips in equipment covered with a black blob like in these pics.This is a DMM, I am trying to take the output to feed into a MCU. Do you how to go about this?When the IC is covered like have you successfully removed the blob to reveal its markings?The front and specs of the meter are athttp://www.canadiantire.ca/en/pdp/mastercraft-digital-multimeter-0520060p.html#.Ut0qhBAo7cs

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 20, 2014, 02:40:49 pm
content: Hi,This type of construction is called Chip On Board, COB. The silicon chip is attached to the PCB and the bonding wires are used to connect the chip to the board. This is then covered with epoxy.The pads around the 'blob' are either for alternative package part and/or test points.This kind of construction is found in consumer products.Jay_Diddy_B

author: minibutmany
author_rank: Regular Contributor
timestamp: January 20, 2014, 02:46:19 pm
content: It looks like jay beat me to it while I was typing. If you tried to remove the blob you would find a bare die without markings. I would try and find a schematic of the product, that may be able to tell you what each of the traces are for.

author: ModemHead
author_rank: Frequent Contributor
timestamp: January 20, 2014, 04:08:24 pm
content: Chances are you will find some version of a 7106 under there, since it's basically a dressed-up 830B. Although the QFP version of the 7106 is usually 44-pin. Maybe the pin numbers match the 40-pin DIP version? Look for a slow clock (50-ish Hz). It's the LCD backplane, which is pin 21 on the 40-DIP.

author: GEuser
author_rank: Frequent Contributor
timestamp: January 20, 2014, 06:24:19 pm
content: Every time I've tried to remove the blob it breaks and rips the chip off too ..

author: Rigby
author_rank: Super Contributor
timestamp: January 20, 2014, 06:51:04 pm
content: Quote from: GEuser on January 20, 2014, 06:24:19 pmDissolve the blob instead of physically ripping it off. Ben Kraznow has a.

author: ablacon64
author_rank: Frequent Contributor
timestamp: January 20, 2014, 11:46:37 pm
content: I've never had success removing that blob also. I've tried Ben's tips a while ago but the chip was ruined anyway.

author: LukeW
author_rank: Frequent Contributor
timestamp: January 21, 2014, 02:44:11 am
content: I'm a bit skeptical that IC "decapping" style procedures with nitric acid would be practical on a COB board, without also destroying the tracks on the PCB or the surrounding components.

author: free_electron
author_rank: Super Contributor
timestamp: January 21, 2014, 04:32:20 am
content: Why would you want to decapsulate it i. The first place ?If it works leave it alone. If it's broken, throw it away. You can't get a hold of bare die's and even if you could you don't have access to bonding equipment so it is fruitless.As for figuring out what it is and who makes it : do you care ? If the meter works let it be. There is nothing you can modify or learn from these complex integrated devices. Even if youhad the datasheet there is nothing you can do with that information.

author: GEuser
author_rank: Frequent Contributor
timestamp: January 21, 2014, 10:42:42 am
content: Quote from: free_electron on January 21, 2014, 04:32:20 amHa Ha , there is a "secret" under that blob , like some here I wanna look!

author: GEuser
author_rank: Frequent Contributor
timestamp: January 21, 2014, 10:51:02 am
content: Also sometimes when I've got half a blob off I've come across the chip is not on tracks but each chip leg is joined close by with very fine bits of wire , like real real fine stuff ..I've also noticed when one has failed to work or does not work correctly the reason quite alot seems to be green stuff like the battery acid green stuff on old alkaline battery's is around the chip under the blob but of course it was wrecked taking a look ..

author: Kjelt
author_rank: Super Contributor
timestamp: January 21, 2014, 10:56:32 am
content: Quote from: Merlysys on January 20, 2014, 02:28:25 pmyou scope the outputs which are conveniently padded in your case to support another casing of the ic and see if you can make any sense of it. Hoping to find something like a serial output signal. But if it is (as suggested above) a 7106 kind of device the outputs are only the lcd segments. You then have to demultiplex the segments to regain the original value.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 21, 2014, 05:37:01 pm
content: Hi,Since the OP reason was to try and interface to the DMM rather than do a teardown. He might want to start with a meter that is fully documented. The Fluke 8050A is one such meter.Here is a project that changed the LCD display to 320 x 240 display.https://sites.google.com/site/kenselectronicsprojects/fluke8050a_displayThe 8050A meter is very solid and very stable and plenty of room inside the case for mods.Just remember the circuitry is reference to the common input terminal, so you will need some form of isolation.Regards,Jay_Diddy_B

author: Rigby
author_rank: Super Contributor
timestamp: January 21, 2014, 08:20:28 pm
content: Quote from: free_electron on January 21, 2014, 04:32:20 amThis is actually a really good point. It is pretty pointless to futz with CoB blobs or anything that is underneath them, unless you're trying to reverse something for a really good reason, in which case you'd know exactly how to do it and wouldn't ask here.If you're just curious what things look like under there, google images can probably satiate that curiosity.If you want to decap your own stuff, harvest some chips from old TVs or something and have a go with those. Unless you know how to design chips, what you see probably won't make a whole lot of sense.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 21, 2014, 08:53:02 pm
content: Quote from: Merlysys on January 20, 2014, 02:28:25 pmGeez, I almost missed this thread due to the title.Anyway, most of Canadian Tire's multimeters are made by Colluck. The model you listed above is a Colluck HH2103Ahttp://www.colluck.com.hk/diyhp/9359/enus/c-25520/p-AAAV+EAAhAAAMdxAAS/Mini_Digital_Multimeter.htmlAs modemhead writes, it is likely some variation of the 7106 (an IC that Fluke and Intersil developed).A note to non Canadians. Yes, $20 (sometimes on sale for $10) is what a cheap multimeter here costs at retail prices. We don't have any $3 Harbor Freight multimeter deals in the big stores. Even the cheap 830 is around $15 in Wal-Mart Canada.

author: Macbeth
author_rank: Super Contributor
timestamp: January 21, 2014, 09:19:25 pm
content: A lot of those blobs secrets can be revealedat ic-fortune.comNot sure of OP's particular meter, but most China "Fluke" knockoffs certainly use these chipsets. e.g. my own VC99 doesn't officially support backlight and RS232, but they can be easily added.OP's meter looks really cheap so maybe not up to the spec of a VC99. It costs around the same.Don't know what you are really after, but why not just use a documented panel meter for a few dollars? Or the infamous $3 meters (830's)

author: ablacon64
author_rank: Frequent Contributor
timestamp: January 21, 2014, 10:33:23 pm
content: Quote from: Rigby on January 21, 2014, 08:20:28 pmMy thought was to replace it with some compatible part, removing it without damaging the board. I have seen those blobs on a lot of main boards and the equipment is lost because of that.

author: w2aew
author_rank: Super Contributor
timestamp: January 21, 2014, 11:32:35 pm
content: Quote from: ablacon64 on January 21, 2014, 10:33:23 pmUnfortunately, you probably would not be able to achieve this. Under the glob is a bare unpackaged die that is likely epoxy die-bonded to the PCB, whose I/O nodes/pads are electrically connected to circuit board traces using bond wires, typically 0.001" diameter gold or aluminium wire that is ultrasonically or thermalsonically bonded to the bond pads and circuit leads. These processes use specialized equipment that few possess outside of dedicated manufacturers. And, it would be very difficult to obtain a bare die replacement in the first place.

author: ablacon64
author_rank: Frequent Contributor
timestamp: January 21, 2014, 11:47:01 pm
content: Quote from: w2aew on January 21, 2014, 11:32:35 pmThanks for the reply. Not a bare die, but maybe a QFN? The pads are there, at least in the boards I've seen.

author: w2aew
author_rank: Super Contributor
timestamp: January 22, 2014, 12:25:12 am
content: Quote from: ablacon64 on January 21, 2014, 11:47:01 pmI suppose it's possible, but I've never seen an epoxy glob top such as this used to encapsulate a QFN or any other SMT packaged part. The pads on the board for COB will look a lot like QFN pads when viewed with X-ray or similar.

author: Nerull
author_rank: Frequent Contributor
timestamp: January 22, 2014, 02:53:07 am
content: Many blobs have pads for a packaged version of the chip around them, that could be what he is referring to. The board in the OP appears to have QFP lands surrounding the blob, for example. I would imagine prototypes tend to use packaged chips - I can't imagine COB is cost effective until you're ready for huge volume.

author: free_electron
author_rank: Super Contributor
timestamp: January 22, 2014, 05:49:26 am
content: Quote from: GEuser on January 21, 2014, 10:42:42 amthere is no 'secret' under that blob. it's just a bare piece of silicon bonded down to the PCb. that piece of silicon contains transistors, diode, caps and resistors. nothing secret there.i don't understand why you think it is secret. if it was a secret device you wouldn't have it in your meter .@nerull : bingo. the protos were probably packed in cerpack or CLCC with a lid. once they got the thing working to switched to bare die. bonding protos is very difficult and costly. COB is only cost effective for mass volume. it is esier during prototyping and development to put the protos in cerpack and solder those down. you can then swap em out while doing testing or even using sockets.

author: Rick Law
author_rank: Super Contributor
timestamp: January 22, 2014, 06:15:57 am
content: Quote from: free_electron on January 22, 2014, 05:49:26 amPerhaps the OP thinks it is a regular epoxy packaged IC chip with regular pinouts and all that, and the dark glob was to cover the regular chip so no one knows what chip it is.

author: MrAureliusR
author_rank: Unknown
timestamp: January 22, 2014, 07:44:09 am
content: The word 'secret' is being used differently than usual here. Another weird English thing. He doesn't mean secret as in restricted, kept hidden, etc. but more as in wanting to discover something new -- 'the mysteries within'. Yeah you can look at images etc. but decapping it yourself is always more fun, plus it's cool to actually see the bondwires etc. Until you see them in real life it's hard to appreciate just how amazing ICs really are.Yes, you could discover the same things by decapping any IC. But I've always wondered what's under the blobs -- it must be interesting to see the bare die with bondwires going directly to pads, instead of inside the plastic packaging that's usually surrounding it.If you don't understand why someone would want to do this...there's not really any explaining it.

author: GEuser
author_rank: Frequent Contributor
timestamp: January 22, 2014, 01:22:46 pm
content: Quote from: MrAureliusR on January 22, 2014, 07:44:09 amThanks for typing that up and well worded unlike what I would respond as , as I really dislike those anti hands on bookishAnalNerdBurglars that have "opinions" who still wouldn't get it no matter what imo , cheers ...

author: MrAureliusR
author_rank: Unknown
timestamp: January 22, 2014, 02:44:36 pm
content: Quote from: GEuser on January 22, 2014, 01:22:46 pmI'd say that's taking it a little far... free_electron in particular is just being practical about it. He's taught many, many beginners to electronics and so just suggests you spend your time learning more useful things. I agree; I'm just saying as a side note it can be entertaining and slightly informative to open up the blobs.

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: February 07, 2014, 06:31:40 am
content: I have one of the mastercraft DMMs in question I'll take it apart AND turn it on (take that Dave) and see what I can find.

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: February 07, 2014, 07:36:54 am
content: Just finished investigating, most of the traces look like they are for driving LCD segs. Some are obviously for measurement input but no unused serial connections.

author: SeanB
author_rank: Super Contributor
timestamp: February 07, 2014, 06:08:30 pm
content: Youwill find 2 unconnected pads at the left side of the pattern of pads that are the serial port connections. As the traces are not going under the blob there is no way to get IR data out of it short of decapping the blob which is likely to be terminal. otherwise you need to pop it off and put the right Cyrustek DMM chip in there instead. At that price it would be better to buy one with the IR onboard though.

author: Monkeh
author_rank: Super Contributor
timestamp: February 07, 2014, 06:48:40 pm
content: Where is the assumption that it's a Cyrustek or Fortune IC and that it has serial coming from?

author: SeanB
author_rank: Super Contributor
timestamp: February 07, 2014, 06:53:49 pm
content: I have seen ( and bought) the cheapies that have a bigger brother with the same features and identical specs but with serial output. Looking inside you see the same COB but with the 2 pins connected and fitting the Cyrustek pinout for the DVM chip in question. The cheapie has a close to identical COB but those pins are not brought out via bonds to the pads.

author: MatCat
author_rank: Frequent Contributor
timestamp: February 07, 2014, 06:55:13 pm
content: I am curious, you can't find bare die on Digikey, so I assume the companies that do mass production get them directly from the manufacturer? Has anyone here actually done any design work using a bare die, if so what is considered the magical production number to make it financially viable? (Obviously you need to be able to bond the wiring, which I am sure is some amazingly expensive equipment).

author: Monkeh
author_rank: Super Contributor
timestamp: February 07, 2014, 06:55:28 pm
content: Quote from: SeanB on February 07, 2014, 06:53:49 pmAnd if you look at this one you'll see all the pads bonded, all of them used, and nowhere for an IR LED to be connected. You'll also note that at 40 pins, it matches the pincount of a 7106/7136, and the various Fortune or Cyrustek chips are all 64-pin or bigger (except the.. 7106/7136 clones!).

author: tom55
author_rank: Newbie
timestamp: April 17, 2024, 11:59:12 am
content: Quote from: minibutmany on January 20, 2014, 02:46:19 pmremoved one from dt830b and it's true. this doesn't help me at all.i have dt9208a that needs new chip, this revision XT9208B, GND pin is the most right in a bottom row. ICL, intersil, AME etc. pinouts do not matchanyone knows what to put here?

author: magic
author_rank: Super Contributor
timestamp: April 17, 2024, 07:42:29 pm
content: These chips support extra features like low battery indication or HOLD which IIRC were not present in "Western" 7106 type chips.Based on this, I concluded that they are likely specialized Chinese chips from unknown vendors, not widely available and with no datasheet unless you are UNI-T ordering a million of them.editMany new DMMs use other chips with delta-sigma ADCs, autoraning and stuff. But the DMM above is probably traditional 7106-style because it contains a film capacitor, footprint for a trimming pot (newer chips would have a calibration EEPROM instead) and seems to be manual ranging.edit editThis looks like QFP44 footprint, doesn't it? I went to AliExpress and found a few offers of ICL7106 in this package. Maybe worth giving a try just to see what happens.Or fork out $10 for a new DMM.

author: tom55
author_rank: Newbie
timestamp: April 18, 2024, 11:09:34 am
content: actually i looked up aliexpress and ebay, found the identical one as i have, ordered at aliexpress - listing said last item in stock, a month later empty bag comes...just two days ago i got dmm ordered on ebay, and of course it is not the same one although looks almost identicalthe idea was to first test both energizer batteries in new unit (as i've previously seen some batteries are just not good for this device) and then compare measurements on PCBsthe thing i received works on AAA batteries, PCB is different without external IC components, in general i don't like it: screen tries to follow up with fancy models by adding unnecessary AC,DC,ohm, buzzer etc symbols ending up in reducing actual digit thickness, but worse than that is viewing angle is practically uselessit also auto shuts down every 10 minutes, even if it is in use during that time. and makes a lot of annoying beeping, before auto shutdown and while changing range. when i only want it to beep in continuity mode. plastic casing looks of worse quality than earlier revision as well as sticker on top of it with all the range indicators (i did not even realize this is a sticker, because it looked way more realistic on earlier revision, until i noticed this on new unit). the item is the same as on attached photo, just without any logo on top, only DT9208A printed (PCB is XT9208V2)definitely need to repair my old unit, no way i can use this and be happy with it

author: coromonadalix
author_rank: Super Contributor
timestamp: April 18, 2024, 11:39:30 am
content: i too was always curious about theses blobs but as written you may need some acid ... etc ... to get to it, i tried acetone it wont dissolve lollit like ceramic epoxyreally hard ...see picture from the web

author: tom55
author_rank: Newbie
timestamp: April 18, 2024, 12:30:08 pm
content: yeah, you need way more dangerous stuff than acetone. i took mine off with scalpel and hot air. was useless anyway as the dt830b was damaged too

author: magic
author_rank: Super Contributor
timestamp: April 18, 2024, 06:29:13 pm
content: Flame turns the epoxy into something akin to charcoal which is easily removed afterwards, if you don't mind ruining the PCB.