Лако-красочные материалы — производство

As stated earlier, the main requirements for adhesives in the electronics industry result from the increasing miniaturization of the electronic devices, which is manifested in an increasing number of pins with decreasing distance between them. Therefore, both the number of leads per square unit of the circuit board increases and the conductor width decreases. Additionally, the “concentration” of devices on the board increases. Further requirements on the adhesives arise from the necessity of reaching high production rates using a simple technology with low energy consumption and of dealing with substances that are harmless for health and environment. From all these facts the following primary requirements result:

1. Precise casting and dosing of the polymeric material is necessary to ensure electrical insulation between the conducting tracks on a PCB. Additionally, the adhesive should not shrink or creep irreversibly during manufacture of electric circuits (e. g., heating by soldering or curing processes, mechanical stresses by automatic insertion). For these reasons, the thermal expansion coefficients of the adhesives should be in the same range as those of the devices and the PCB.

2. The increasing quantity of power dissipation per square unit as a result of the rising density of devices on PCBs leads to higher operating temperatures. Therefore, the thermal resistance of the applied adhesives has to correspond with the operating temperatures. Furthermore, a low dielectrical constant is essential for the adhesives and/or binders used for laminates because the heat dissipation is a result of dielectrical losses.

3. Up to now the electrical connection of devices and conducting tracks is made by solder processes, and therefore the adhesives have to withstand temperatures of about 260°C for a short time without remarkable losses in their performance. Up to now, conducting adhesives for electrical connections as an alternative have been used in special applications only.

4. The adhesives have to show adjusted rheological behavior. Depending on the application, materials with both high and low viscosity, with and without thixotropy, and with and without yield point are needed.

5. Since electronic circuitries have a filigree structure, they are sensitive against corrosive media. For this reason they must be covered with coatings or sealants of high purity. Alkaline and chloride ions and residual solvents especially have to be avoided.