Cob

[Don Larisey]

I may have to do some designs with chip-on-board and I don't know where to start. I have been doing some searching on the internet, but I seem to be getting a lot of general stuff. I am looking for info such as wire bond pad sizes, spacing, trace sizes, etc. And any other info related to layout of COB.
Regards,
Don

[randychase]

Don,

I have done a bit of COB using PowerPCB with good results. I found the best data was to use the standards from the company that is going to do the wire bonding. When my clients used different assembly shops, I received a different set of standards.

These standards include:
1. Die Attachment Pad size and voltage potential of DAP.
2. Min Bond Pad size.
3. Max angle of attachment wire.
4. Min/Max distance of wire points.

Then you will need a diagram, drawing, or spreadsheet showing you the locations of the wire bond points on the chip. Then it's just going thru and determining the proper die pad locations based on that data. I create a part like this. Typically it will have a DAP (speaking in mils) of maybe 100x100 up thru .500 x .500, tied to GND or VCC. The pads will be around 6-10 mils square and with a suitable gap to the DAP.

I recently did some boards also with COB transistors and diodes. It's interesting doing this small scale pcbs, like a something that fits into a wris****ch but has a microprocessor.