Condensation silicone potting compounds is a common material for potting electronic components, for people who just contact often encounter some puzzling problems, resulting in the potting of electronic components are always a variety of problems. The following is a summary of the common problems and solutions of condensation silicone potting compounds are discussed.
1. AB Ratio
The amount of curing agent and temperature changes, etc. have a greater impact on the curing speed, the amount of curing agent increases, which will accelerate the curing reaction. Condensation silicone potting compounds curing process, there are small molecules generated, not suitable for heating curing, otherwise it makes the small molecules volatilization speed up, resulting in expansion phenomenon.
Usually the ratio of part A silicone and part B curing agent is 10:1, the recommended range is 10:0.8-10:1.2 (weight ratio). If you need to change the ratio of AB, please do a small amount of test on the changed mixing ratio in advance, in order to check whether it is suitable for your project.
It is recommended to use low viscosity and longer operating time silicone potting compounds raw material, so that the air bubbles can be eliminated automatically before letting the liquid silicone material curing. The curing temperature should be controlled within 45℃ to avoid the high temperature to produce a large amount of ethanol gas in a short period of time, thus creating bubbles.
3. Partially Uncured
If part A and part B are not stirred evenly will cause part of the slow curing or not curing phenomenon, so it must be stirred evenly.
In order to enhance the performance of silicone potting compound thermal conductivity and flame retardant usually add some thermal conductivity powder and flame retardant powder, after a period of time the filler may appear to settle at the bottom, the surface will appear a layer of colorless transparent silicone oil, such as direct use without mixing evenly may cause the surface color grayish, long operation time, surface sticky, etc., so before use, we must first stir and mix the A part separately.
The common fillers are inorganic powder, and in the field of silicone potting compounds, the common powder is silica micronized powder. Compared with silicone oil, the density is greater, and the surface-active group is less, and the compatibility with silicone oil is poor, so as the resting time becomes longer, the inorganic powder gradually settles, causing the separation of oil and powder.
5. Yellowing of the Curing Agent
In order to ensure that the silicone potting compounds to PC shell, PCB circuit board has good adhesion, the general use of ammonia coupling agent to improve the bonding, so placed about 2 months, the color of the curing agent will be yellow, but this does not affect the curing time and product performance.
6. Reduction Phenomenon
Higher fatty acid tin is one of the most commonly used catalysts for this reaction and will hydrolyze to alcohols in the presence of water and catalyze the reaction to occur rapidly. However, there is a reaction equilibrium in this process. Under certain conditions: high temperature and airtightness, The presence of moisture or alcohol will cause the reverse reaction of the curing reaction, that is, the reduction phenomenon.
7. Removal and Cleaning
Before the silicone potting compounds are cured, you can use a clean cotton wipe to remove the uncured liquid silicone material, and then use a solvent such as isopropyl alcohol to clean the residue. After the silicone potting compounds are cured, the silicone can be scraped off with a knife, and then various residues can be removed using solvents (120# solvent oil, alcohol, xylene and acetone, etc.), soaked and decomposed.