1. Conformal Coating Pretreatment
Conformal Coating is nowadays known as the effective method for protecting Printed Circuit Board from adsorption of atmospheric moisture, contamination of the surface with airborne ionic material, electrostatic attraction of dust to the surface, condensation in last stage of manufacture.
♦ So why should we use Plasma to pre-treat the PCB surface before applying the Conformal Coating?
It should be remembered that conformal coatings do have their limitations. Any contaminants present on the surface before conformal coating will be sealed in by the operation and may cause long term problems – such contaminants might include fingerprints, flux residues, and moisture and other atmospheric pollutants. Boards should always be cleaned and dried before conformal coating to obtain optimum long-term performance. As a result, choosing a good pre-treatment for surface is as important as choosing the method protection.
♦ Benefit of Plasma Conformal Coating Pretreatment
- Improve the surface cleanliness of the circuit to protect against corrosion and the effects of contamination on the surface from the process.
- Activate the surface of a PCB board and a surface-mounted component
- Improve the surface energy of the surface to improve the adhesion of conformal coating
♦ Features make Plasma more advantageous over the traditional methods
Traditionally, cleaning and adhesion promotion have been achieved by either using a wet chemistry treatment like washing or applying extra undercoats (priming). However, these methods have some limitations while Plasma could solve them:
- Environmentally friendly method
- Ability to treat complex 3D objects and micro-channels that hard to reach with normal methods
- Both cleaning and activating the surface just in one step
- Treat conductors, semi-conductors, and insulators which all are small and dedicate and difficult to bond
- Cost-saving with low unit cost per treatment
- Ability to produce high value-added property to product as using new technology
2. Power Modules Impregnation process pretreatment
Power modules using power semiconductors, various sensors requiring hermeticity, and spark plugs used in automobiles go through an impregnation process in which the inside is filled with resin with high viscosity, such as silicon and epoxy. In this process, the plasma treatment greatly reduces the possible void swelling (a phenomenon in which unwanted air still remains).
3. Surface cleaning prior to wire bonding
Atmospheric pressure plasma is used in wire bonding as a selective fine cleaning step to remove contamination and residues from the contact surfaces. In general, strong bonds between wire and substrate can only be achieved on clean contact surfaces (bond pads).
In practice, there are often contaminations on the surface, which can result in non-stick on pad or so-called “lifts” (elevations of the bonds). Both cases lead to failures, downtimes, and quality defects in production.
For this reason, atmospheric pressure plasma is used in this process for selective fine cleaning prior to wire bonding, which avoids non-stick on the pad as well as lifts and increases quality.
4. Plasma for oxide removal
The use of foaming gas from Plasma helps remove the oxide film, thus providing a more stable soldering environment and making the reuse of expired products possible. It also improves the wettability of surface for soldering process.
- The Surface of Lead Frame
- The Surface of DBC and Heat-sink
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