What secret lies under that blob?

[Merlysys]

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 at http://www.canadiantire.ca/en/pdp/mastercraft-digital-multimeter-0520060p.html#.Ut0qhBAo7cs

[Jay_Diddy_B]

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

[minibutmany]

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.

[ModemHead]

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.

[GEuser]

Every time I've tried to remove the blob it breaks and rips the chip off too ..

[Rigby]

Every time I've tried to remove the blob it breaks and rips the chip off too ..

Dissolve the blob instead of physically ripping it off.  Ben Kraznow has a .

[ablacon64]

I've never had success removing that blob also. I've tried Ben's tips a while ago but the chip was ruined anyway.

[LukeW]

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.

[free_electron]

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.

[GEuser]

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.

Ha Ha , there is a "secret" under that blob , like some here I wanna look!

[GEuser]

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 ..

[Kjelt]

This is a DMM, I am trying to take the output to feed into a MCU. Do you how to go about this?

you 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.

[Jay_Diddy_B]

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_display


The 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

[Rigby]

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.

This 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.

[retiredcaps]

The front and specs of the meter are at http://www.canadiantire.ca/en/pdp/mastercraft-digital-multimeter-0520060p.html#.Ut0qhBAo7cs

Geez, 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 HH2103A

http://www.colluck.com.hk/diyhp/9359/enus/c-25520/p-AAAV+EAAhAAAMdxAAS/Mini_Digital_Multimeter.html

As 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.

[Macbeth]

A lot of those blobs secrets can be revealed at ic-fortune.com

Not 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)

[ablacon64]

Unless you know how to design chips, what you see probably won't make a whole lot of sense.

My 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.

[w2aew]

Unless you know how to design chips, what you see probably won't make a whole lot of sense.

My 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.

Unfortunately, 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.

[ablacon64]

Unfortunately, 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.

Thanks for the reply. Not a bare die, but maybe a QFN? The pads are there, at least in the boards I've seen.

[w2aew]

Unfortunately, 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.

Thanks for the reply. Not a bare die, but maybe a QFN? The pads are there, at least in the boards I've seen.

I 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.

[Nerull]

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.

[free_electron]

Ha Ha , there is a "secret" under that blob , like some here I wanna look!

there 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.

[Rick Law]

Ha Ha , there is a "secret" under that blob , like some here I wanna look!

there 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.

Perhaps 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.

[MrAureliusR]

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.

[GEuser]

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.

Thanks for typing that up and well worded unlike what I would respond as , as I really dislike those anti hands on bookish Anal NerdBurglars that have "opinions" who still wouldn't get it no matter what imo , cheers ...