Such as the title: I believe that domestic LED packaging glue technology has made considerable progress compared with foreign countries, but there are still many problems in high-fold LED packaging glue. The key to solving the problem is to raise the problem and think about the root cause of the problem.
1. Summary of the problems of high-fold LED packaging glue:
1.1 The hardness increases after high-temperature baking. This problem has been troubled for a long time. Some people have suggested that the vinyl reaction steric hindrance of phenyl vinyl silicone resin is relatively large. The general baking process is 80C/1hr+150C/3hrs, and the curing is not complete. After baking at high temperature again (250C/4hrs), the hardness of the colloid increases significantly and becomes hard and brittle. Solution: Someone proposed in the formulation design that adding linear phenyl vinyl silicone oil (linear type) can improve this problem, but other problems also arise. The addition of silicone oil is small and the improvement effect is not obvious. The addition of silicone oil is large. The decrease in the adhesion of the resin is particularly noticeable. After reflow soldering, it will be debonded!
1.2 Poor thermal shock performance: Dow Corning's products have not been tested, but domestic products can achieve 300Cycle (-40C/15min-100C/15min) undead lamps, and there seem to be not many non-degumming. Factors affecting thermal shock performance are Many, 1. The quality of the semi-finished patch is very obvious. The performance of the same glue on different brackets is very different. 2. The factor of glue is related to the formula design of the encapsulant. Of course, this factor is also very complicated. For example, the structure, molecular weight, and molecular weight distribution of the resin used affect the hardness, tensile strength, and tear strength of the cured colloid. . But the main point is that the toughness is good when the hardness is low, but the tear strength is poor, and the thermal shock effect is improved. This has been verified.
1.3 Moisture absorption problem, the specific manifestation, the colloidal solidified block is placed in a place with high humidity, from transparent to turbid, and foggy. The cause of this problem is not yet known, but it is certain that it is related to the resin or tackifier used. Is the hydroxyl content in the resin too high? But I have tried silicone resin with high hydroxyl content, but the cured block does not absorb moisture. I am very confused about this?
1.4 The yellowing problem, I believe that the yellowing problem should have been solved a lot, but due to experimental conditions, it is impossible to measure the light transmittance of the cured block after it has yellowed. Dow Corning test conditions, 150C/7D, measure the thickness of the cured block The change in light transmittance is a measure of yellowing. Dow Corning's patent proposes that yellowing is closely related to the type and dosage of platinum catalysts and inhibitors.
1.5 The problem of tackifiers and fogging of tackifiers has also been solved a lot, but at the same time improving the adhesion of colloidal PPA and metal still needs to work hard, do more basic research, it seems that there are not many products on the market?