Black Blobs - Page 1
Forum section: electronics / beginners

author: oldguyjohn
author_rank: Contributor
timestamp: September 10, 2016, 09:20:20 am
content: Hi All,Can somebody please enlighten me as to the purpose of the black blobs found on some commercial circuit boards?I have prised one off and it doesn't appear to connect anything? The substance does not appear conductive. What are they for?Attached two photos to show what I mean. One circuit out of a digital volt meter, don't know what the other was.Thanks

author: MosherIV
author_rank: Super Contributor
timestamp: September 10, 2016, 09:25:17 am
content: The block blob is the epoxy that cover a silicone device that is bonded directly to the pcb instead of using a chip. This keeps the manufacturing costs down. It is know as Chip On Board or COB.Ver common for very high volume manufactured stuff.The connection to the board would be with very thin wire bonded to the circuit board and then onto the silicone and the expoy the protects the whole thing.Hope you did not need the thing where you ripped it off - it will never work again.

author: brabus
author_rank: Frequent Contributor
timestamp: September 10, 2016, 09:27:27 am
content: https://learn.sparkfun.com/tutorials/how-chip-on-boards-are-made

author: oldguyjohn
author_rank: Contributor
timestamp: September 10, 2016, 01:13:31 pm
content: Many thanks to you both for the replies. I was thinking I should know what was under the blobs in case I could repair anything! Obviously no chance, It's amazing how stupid I can be when first starting out learning a new subject. Fortunately the blob I prised off was only on a junk board so no harm done.Thanks for the link Brabus. Very interesting videos.Another small snippet of knowledge learned.Thanks again.

author: wraper
author_rank: Unknown
timestamp: September 10, 2016, 01:42:11 pm
content: Quote from: oldguyjohn on September 10, 2016, 01:13:31 pmFirst board obviously can be repaired if that blob fails. The issue is that packaged replacement IC may cost as a whole board. PCBs which can accept both packaged IC and COB as well are not rare at all. In that case just remove the blob and solder in new packaged IC. But, of course, you need to know what is that part to buy the right one.

author: amyk
author_rank: Super Contributor
timestamp: September 10, 2016, 02:54:10 pm
content: Quote from: wraper on September 10, 2016, 01:42:11 pmI think the COB+DIP is an ICL7106 because that's a very common arrangement for this IC.

author: Zbig
author_rank: Frequent Contributor
timestamp: September 10, 2016, 03:18:44 pm
content: Fun fact: years back, when PC RAM came in the form of SIMM modules, where I live, the COB-populated ones were called "topless" by some.

author: Audioguru
author_rank: Super Contributor
timestamp: September 10, 2016, 03:22:48 pm
content: Quote from: MosherIV on September 10, 2016, 09:25:17 amNo, silicone is synthetic rubber. It is a silicon IC chip.

author: wraper
author_rank: Unknown
timestamp: September 10, 2016, 03:28:47 pm
content: Quote from: amyk on September 10, 2016, 02:54:10 pmYes most likely it is, more precisely Chinese clone of ICL7106. Finding right multimeter chipset should be one of the easiest situations to figure out what is that IC.

author: Zero999
author_rank: Super Contributor
timestamp: September 10, 2016, 06:37:43 pm
content: Quote from: wraper on September 10, 2016, 03:28:47 pmI agree. It's most likely an ICL7106. It could even be genuine or it might be fake. There's no way of knowing, without repackaging it and comparing it to a genuine ICL7106 die.Plenty of ICs are (or have been) available as plain dies. For example, the TL082Y is the TL082 in bare die form. Here's a link to the datasheet. I don't know if it's still available because the current TI datasheet doesn't show it.http://f5ad.free.fr/Docs_ATV/TL081.pdf

author: wraper
author_rank: Unknown
timestamp: September 10, 2016, 07:03:19 pm
content: Quote from: Hero999 on September 10, 2016, 06:37:43 pmNo chance being original. Too cheap device and there are shitloads of clones. Heck I even have a Soviet time clone (KR572PV5) made here in Riga which I put into one of my DIY devices.