The Cause and Solution When Having Air Bubbles During Potting
We has introduced in previous article about what is COB, what is process of COB, and bonding wire and its pulling force. In this article, we’re going to talk the problem about the air bubbles in epoxy under the production process. It is not allowed to have bubbles exist in epoxy. The bubbles in the epoxy floor not only affect the aspect of the board, but also could damage the stability of AI wire and gold wire from inner wire bounding.
The solution is as follows
When there are bubbles in the epoxy
C- Improper mixing of adhesive and hardener.
S- Careful mixing.
There is air remaining during the process of potting.
C- The speed of potting was too fast or having some problems in the production process.
S- The mechanization can offer quality stability. Additionally, we usually use small needle for production and rotate from exterior to inner, the direction can also be reversed.
The too high viscosity of epoxy.
C- The too high viscosity cause the lack of liquidity and the voids cannot be filled properly. The liquidity increasing happens at the beginning of curing. Firstly the epoxy flows to fill the voids but bubbles are formed on the surface; secondly the air still cannot overflow completely and internal bubbles will be formed.
S- Find the epoxy which is low viscosity to increase the liquidity, or pre-heating the epoxy.
The inappropriate conditions of epoxy curing
C- The over temperature of curing cause the faster curing time, however, it also decrease the possibility of overflowing the bubbles from epoxy.
S- Do not increase the temperature to shorten the time of curing.
*Related Article:
COB2:Brief Introduction Process of COB (Chip On Board)
COB3:Introduce COB's bonding wire and its pulling force