Author：Alan Zhang
The main purpose of conformal coating is to make PCBA insulated, waterproof, and protected. It mainly is used on outdoor applications, such as motor PCBA, solar controller, traffic signs controller, ships, etc. Because the products above mentioned are subject to rust due to humidity, dust, and sunlight, they get short-circuited problems the normal use time is shortened, so conformal coating provides a solution to prolonging life.
1. There are two main materials in the market for conformal coating process. One is acrylic the
other is silicon/rubbe.
A). Acrylic series: It becomes a harder and more wear resistant after drying. And it is transparent.
It is the most widely used material and it is heat resistant up to 120℃.
Advantages: high abrasion coefficient; re-fixing is easy.
Weakness: Low resistance to chemical solvents.
B). Silicon series: It is soft a, heat resistant up to 180 ℃, it has good toughness. It is commonly
used in outdoors and places with high temperature.
Advantages: highly resistant to heat; good flexibility.
Disadvantages: less abrasion coefficient easily gets scratches and peeled off
2. Coating thickness based on IPC-A-610 standard
A). Acrylic AR (Acrylic resin) 30 - 130 μm
B). SR (Silicone resin) 50 - 210 μm
3. Coating processes are described as below:
A :Soaking
Advantages: low cost; operation is easy; high producing capacity.
Disadvantages: coating thickness can't be controlled; it is applied to single board only;
material is subject to pollution.
B :Brushing
Advantages: low cost; operation is easy, medium producing capacity.
Disadvantages: coating thickness can't be controlled; the quality is hard to control; manual
protection is required.
C. Spray by robotic arm
Advantages: medium cost; coating thickness can be controlled; high producing capacity.
Disadvantages: higher material loss; manual protection is required.
D. Automatic shower
Advantages: coating thickness can be controlled; auto machine operation; medium
producing capacity; more materials saved; no manual protection is required.
Disadvantages: high financial investment in the initial stage.
4. Market trend and demand
A. Precise dodge and spraying.
B. Standard coating thickness.
C. Record ability and tractability for production status.
5. To cope with production of low volume high mix and to meet customers' need, PSI is following the procedures:
A. Soaking: Applied to single board or boards without DIP parts on the back side. PSI does
not apply this operation.
B. Brushing: Applied to partial coating or small boards with low volume. PSI does this
operation manually
C. Spraying by robotic arm: PSI sub-contracts the job to our partners for the boards under
special requirement for thickness and appearance.
D. Automatic shower: Work with firms providing the equipment for prototype production.
To sum up, there has been more and more demands on conformal coating from our customers nowadays, but some demands are not actually needed (because the company can't discuss with customer directly on this). It results in the company being not able to apply a proper operation for mass production, and it also leads to a dilemma between current running operation and standard operation. PSI has lots of experiences from the past, and has a good cooperation with material suppliers and equipment suppliers. For different needs from various customers, PSI can rapidly adjust its operation to meet the customers' demand. Based on professional standard, both (PSI and the customers) can discuss with each other and reach the best result of product protections.
For example, the Apple Inc. uses partial coating to make their products waterproof. Coating for a majority of areas is applied to the cameras. In addition, we need to consider the issue on the dissipation of heat. (Those components which require heat dissipation can't have conformal coating). The coating can really protect electronic products' life, and the process becomes more and more refined. Yet, we still have to make sure the process and the purpose by discussing them with the customers, in order to get a win-win situation. Protect components which really need protection to save material and labor time cost. Furthermore, we can reduce our cost, extend product life and let more customers accept conformal coating. Eventually, end customers and users can enjoy using electronic products of good quality.
