Do you have a Chip On Board?
We've all gotten them. You open up that greeting card from friends or family, and are bombarded with a tinny sounding version of happy birthday or "Old Lang Syne". In my case, the battered card to the left was from my sister, and the song was an amazingly good sounding version of "Jingle Bell Rock". Like any good engineer, I set it aside to be dissected later.Once I peeled back one side of the card, I was surprised to see a rather nice miniature speaker along with the expected circuit card. The PC card and speaker were pre-mounted to a sticky-backed piece of cardboard that could easily be mounted into the guts of any greeting card. Opening the card yanks on the low-tech contact switch on the upper left side of the PC board.
The electronics are simple. One sound IC (more on that later), 2 resistors (5.1K and 375K), a capacitor (47uF), 3V lithium coin battery and make shift switch rivetted to the PC board. The PCB itself is single sided. Resistors and caps are through-hole mounted and soldered.
The IC itself is under that black blob of epoxy you see in the photo. This type of mounting is sometimes referred to as a "blob-top". Another, more technical, term is "Chip on Board", or COB.
Sound modules like the one shown are available with a range of features and prices. We found modules available for as little as 60 cents in volume. If you're thinking of going into the greeting card business, you might checkout some of the following sources:
- One Time Recordable Greeting Card Module at VTK INDUSTRIAL LTD
- MUTR Greeting Card Module
- Selection of card modules from http://www.alibaba.com
- National Artcraft.com has modules from 60 cents in volume
Most of the suppliers we found were based in the far east, and technical specifications for the modules are not available on the web. The blob-top packaging on our sample prevented us from determining any specifics on that particular IC. If you would like to learn more about this particular area of interest, a good source is Frank Ostrander's The Serious Business of Sound for Toys. One of the sources that Frank mentions is ISD's ChipCorder product. An aside: ISD was acquired by Winbond Electronics Corporation in 1998.
Argo Transdata Corporation has a brief slide presentation which explains the "chip on-board" process. If you would like to go into more detail, National Semiconductor has an archived web seminar available on the subject of Chip On Board assembly processes. The material is a bit dry, but the SEM photos and illustrations are extensive, and speaker goes into quite a bit of detail on subjects such as shipping media, choice of substrates, die attach, coexistence with SMT components, wire bonding, and encapsulation.
The final photo shown here is of the backside of the same PCB shown above. Recall that this is a one-sided PCB. In this photo, which has been enhanced a bit with Photoshop Elements, you are viewing the metal layer through the PCB material. It's easy to see where the die and wirebonds are attached on the flip side of the board.
Hallmark Cards meets electrical engineering. Who would have guessed? This example again illustrates how pervasive electronics are in our life, as well as the fact that as engineers, we can learn something from even the simplest examples.