Chip On Board Manufacturing

The Black Blob on PCBs

Have you ever wondered what the black blob on the calculator or Remote or any other electronics PCB does, or at least is it any part or is it a misfired glue blob from the hot glue gun turned black!!!

This is a picture of a 16X2 LCD module with Chip On Board [COB]

Its actually called Chip On Board or [COB], and the black blob is the protective covering given to the bare bone chip which is the brain of any device that is in.

COB Manufacturing

Shown above is a tray of controller silicon dies that serve as the brain of the multimeter

The first step is to glue the silicon die to the PCB. I’m not entirely sure if the adhesive is conductive or not, but, judging by the exposed pad, it probably is.

With a pair of tweezers the dies are placed by hand(!). The adhesive sets within 5 minutes. This was another moment that caught me off guard.

I assumed COB required a clean room with precision tools and ultra-accurate placement. It turns out, just like SMD soldering in a hot plate, you can have a lot of variance and still have a fully functional board.

The PCB is then inserted into an amazing automated wire bonding machine that bonds a very thin wire from the IC to the PCB.

You can see the operator has to tell the visual recognition system a few alignment spots once in awhile, but in general, the machine quickly solders all the connections.

In this picture you can clearly see the Silicon chip connected to the pad by a mesh of wires.

Forty one connections later, and the die is all connected up. As you can see, the small theta rotation of the IC doesn’t make much of a difference.

A assembler squirting a small dab of potting compound over the entire structure.

The next step is to squirt a small dab of potting compound over the entire structure. This material electrically and physically protects the die and wire bonds from damage.

The viscosity of the compound must be tightly controlled to prevent the hairs from bending over and connecting with neighboring wires.

The liquid compound is then cured in an oven for four hours. Once complete the boards are tested and continue down the process of becoming a multimeter.

My story right now.

• I finished designing my PCBs for my final year Engineering. :)
• Doing my internship in a Aerospace R&D company. It’s exciting.
• Covid-19 Pandemic.
• Stay home. Stay safe. :)

Make your own hand sanitiser.

Materials required :

1. 70% Iso-propyl Alcohol(IPA) (Rubbing Alcohol)
2. Water
3. Glycerine(Optional)

Steps:

1. IPA mixed with water. You can use a atomiser bottle for ease of use
2. IPA : Water = 70 : 30.
3. Stay safe. :)

See you next time

SS

Thanks for reading.

Until next time

Peace, Love and Gratitude.