COB Black (Epoxy) is usually not allowed, because the external air hole will not only affect the appearance, the internal gas hole is more likely to break the wire bonding aluminum stability. Even when the cob process is complete, there is no functional test, it does not mean that there is no problem, because after a period of time, it is very likely because of the gas Conne hot hyperinflationary cold contraction of the role of the aluminum line (AL wire), and the internal gas hole may also accumulate water, Over time, the part of the internal line of the oxidation impact function.
There are a lot of reasons why black can produce bubbles, and the solution is not necessarily to start with the reason why the black gel may produce bubbles. The black gel itself is not very likely to produce gas, so the formation of the gas hole is generally the following several reasons:
- There is a mixture of air in the black gel.
This is probably from the stirring of the black gel. Can be seen to continue to explain.
- The air envelope is less than escaping when filling.
If the speed is too fast or the filling process is not right, it is easy to seal the air in the black, and if the viscosity of the black gel is higher, air is not an opportunity to discharge, can only be kept in the inner part of the seal to form a bubble.
The process of potting is best handled by the machine, and can have a more stable quality of the filler, in addition, the general process of filling with small needle tube, you can start from the outside to the inner circle to complete, or vice versa; avoid a large amount of potting from the middle, or it will form a shadow effect between parts and parts, so the most common place to develop bubbles is in the wafer ( Dice) to the junction of the circuit board (PCB) or the welding at the aluminum line.
- the viscosity of the black Gel (viscosity) is too high.
If the viscosity of the black gel is too high, the mobility will be insufficient, it is not filled with sewing gap in the place, until the beginning of the initial flow of baking increased, a black fluid filled with the original gap, but the surface of the formation of bubbles; the air is not completely overflow, it will form an internal bubble.
The solution is to find a lower viscosity of the black (epoxy) to increase mobility, or the use of a hot black and a circuit board, Black has a strange and very characteristic, when you add it a little bit of temperature (60~80°c around), its mobility will become better than the temperature, but the heat to higher temperature ( 120~150°c), the flow will quickly decrease and start curing.
- the baking conditions of the black rubber are not exactly
Some people for the sake of fast and the black baking temperature to shorten the baking time, when the temperature of the black baking is high, the curing speed is accelerated, but the opposite also reduces the bubble from the black gel overflow possibility. In addition, the curing speed of black can also cause black brittle problems, but poor quality.
Other things about the storage and operation of the black gel can cause black bubbles:
- After the black gel has retreated, it has expired.
Generally, black is required for low temperature storage, after the ice has been set to run out after the time, if the period will have the possibility of hardening, it affects the speed of the fluid after the injection, the slow flow of black, easy to wafer (dice) and the circuit board (PCB) at the junction or in the aluminum line welding process to produce bubbles.
- Does the black gel roll before use as required by the supplier?
Black is usually added to some other substances that can help to solidify, and after a period of time it is easy to starch (deposited), if there is no rolling process before use, there will be mixed uneven situation, the impact of the quality of the gel, bubble is also one of them.
- The black storage is upside and inverted.
As mentioned in the previous question, the black gel is easy to starch, so it has to be stored backwards (opening the lid below), this is to check if there is a hard block in the starch, and if there is a hard block, you have to smash the pieces and let it blend into the original black, so that the ratio of black ingredients will not run away.
- The black stirring is mixed with a long or uneven mix.
The black glue needs to be stirring to mix the ingredients, avoid the problems that have been caused by the starch, but some of the companies that are not well equipped will be able to mix the stirring with sticks directly, so it is easy to mix the air into the black with the stirring, and the solution is to use the method of rolling stirring mixing or making black gel. , the foam is generally placed in a steel tube that can withstand a large pressure, and then the internal pressure is lowered, allowing the air to overflow from the black gel.
- The black glue is placed in the room temperature for a long time.
After the general grouting is not proposed in the room temperature for a long time, it is easy to let the outside of the black plastic first hardened, and the impact of internal bubbles escape the opportunity.
The cause and solution of the bubble production in COB epoxy
