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I'm looking at high volume manufacturing and I notice that inside some consumer toys, there are chips which seem to be directly placed on the board and covered in resin. I know this has been done a long time because I remember such boards from my childhood in pocket calculators. See the image for a typical example.

PCB Image What is under this resin? Is it a naked chip directly mounted on the board with bond wires to the pcb?

Can someone enlighten me to the name and type of manufacturing process here and tell me anything about how hard it is to use this approach, in terms of working with a manufacturer, and the costs and volumes involved, relative to just using a regular surface mount chip?

JYelton
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Robotbugs
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    Maybe related to (but not quite a duplicate of) http://electronics.stackexchange.com/questions/9137/what-kind-of-components-are-black-blobs-on-a-pcb. – Renan Feb 08 '14 at 01:56
  • Nice that you noticed the other question. I wonder if there are any people who "know" about this process? Also its useful to have a key name "chip on board" as a web search was coming up with nothing. Maybe it should have been obvious but I didn't think of that one. – Robotbugs Feb 08 '14 at 02:11

1 Answers1

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As you commented, it's called COB (Chip-on-board). The layout can be done with a conventional PCB layout program such as Altium,

enter image description here

but the mounting process is done with a different set of equipment from the rest of the assembly (a die bonder and a wire bonder).

enter image description here

Then a glop of epoxy is added over the chip and bonding wires.

The COB process shown in your photos is mostly a high-volume Asian thing, though anybody with the appropriate equipment could do one-offs (if they could source the bare dice, a huge if). The advantage is that you're saving a few pennies on the chip package (and often the chip testing), at the expense of lower reliability.

Often the chips used in this sort of assembly are sold only as bare dice, and are not available in small quantities, nor are they available through conventional distribution. Testing is often not 100%, the assumption being that the testing will take place later, and defective assemblies are cheap enough that they can be discarded (usually there's very little of value on the COB assemblies beyond the chips).

A cousin of COB is COG (Chip-on-Glass), which is used in most color LCD displays. The drivers are on chips that are designed (only) to be directly bonded to the glass. They have extreme physical aspect ratios so you'll not find them in a package.

enter image description here

Spehro Pefhany
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