As we all know, the continuous progress of electronic equipment and circuit technology, the peak of engineering art in the design, development and manufacture of 印刷电路板 （PCB）已经被世界各地的人们目睹了。 Our planet is full of highly intelligent machines, automated robots and scientific marvels, and of course, there are plenty of PCBS in every corner of the planet, no matter what country or city it is. 然而，这些 PCBS 在功能、复杂性、制造成本、质量和可靠性方面确实有所不同。 本文重点讨论最后两点，PCBS的质量和可靠性。

是的，潜在客户总是想要高质量的电子产品，但这非常昂贵，并且可能涉及复杂的制造过程。 在PCB制造、组装和测试的复杂过程中，有一个非常重要的工序叫做PCB的“保形涂层”。 就质量和可靠性而言，这种敷形涂层在 PCBS 中非常重要。

What is conformal coating and its importance:

Conforming coating, an ultra-thin protective coating of polymer film, can be used in conjunction with assemblies mounted on assembly surfaces to protect assembly leads, solder joints, exposed wiring, and other metal points on the PCB surface from corrosion, dust, or chemicals due to various operating or environmental conditions.

保形涂层可以薄至 25 微米，并“符合”电路板的形状和组件布局。 如上所述，在 PCB 的表面（顶部和底部）应用保形涂层的原因是为了保护 PCB 免受不利的外部环境条件的影响，从而增加 PCB 和相关电子设备的使用寿命。

与工业、工厂和大功率电子产品中的高温一样，这些带有敷形涂层的 PCBS 可以承受极端温度。 同样，安装在靠近大海或海洋的地区/地区的电子设备可能会受到高湿度的影响，例如导航电子海军设备可能会受到腐蚀/侵蚀，从而导致金属氧化。 Similarly, in microbiology laboratories and the medical industry, sensitive electronic equipment can be exposed to toxic chemicals, acidic and alkaline solvents that can accidentally spill onto a PCB, but the PCB’s “conformation coating” will protect the PCB and components from fatal injury.

如何应用保形涂料？

In fact, the method of applying “conformal paint” in the right way is so important that careful consideration must be given to how conformal paint is applied. It is as important to choose suitable conformal coating materials.

决定敷形涂料正确应用的主要因素是：

1- 油漆厚度

2- The level of coverage achieved

3- The degree of adhesion of paint to wood panels and their components.

There are five methods for applying conformal coatings:

1-用刷子手工绘画

2- 气溶胶涂层

3- Atomizing spray gun coating

4- Automatic dip coating

5- Automatic selection of coating

三防漆固化/干燥方法：

Conformal coatings themselves can be classified according to the drying and curing methods used after conformal coatings are completed. These methods are:

1- Heat/heat curing: Conformal coating is dried at high temperature. Drying rate is much faster than normal room temperature drying/curing.

2-冷凝固化：PCB的保形涂层在环境温度下干燥，大气中的水分会减慢固化或干燥过程。

3- ULTRAVIOLET (UV) curing: Here PCB with conformal coating is exposed to UV radiation. The uv energy determines the curing speed of PCB conformal coating

4- 氧化固化：在这种方法中，PCB 构象异构体暴露在含有大量氧气的露天环境中，这将有助于溶剂型构象异构体的干燥/固化

5- Catalytic curing: This is the process of curing conformal coating in which two materials are fused together, one of which is conformal coating. 一旦涂层与其他催化剂材料融合，固化过程在完成之前不能停止。

Classification of conformal coatings:

There are five main conformal coatings used: acrylic resin, epoxy resin, silicone, polyurethane (PU) and polyparaxylene coating.

L 丙烯酸树脂（AAR）：

Acrylics are ideal for (low-cost and high-volume) common electronics because AAR is inexpensive and can be easily applied to PCB surfaces by brush, dip, and manual or automatic spraying, reducing turnaround time and producing cost-effective products.

好处

1 – 低成本

2- Easy for manual or automatic robot applications

3- Easy to rework

4- Excellent moisture protection

5- Good surface elasticity, can withstand static voltage discharge, and does not react with the atmosphere, therefore helps cure through solvent evaporation

缺点：

1- Due to the use of atmospheric curing/drying methods for this material, proper ventilation systems need to be ensured

2- 低粘度维护

3- 低耐磨性和耐化学性

L Epoxy conformal coating (ER) :

基于环氧树脂的敷形涂层可以通过手刷、喷涂或浸涂来完成。 建议对较大体积和较小体积或原型 PCBS 进行喷涂。

好处

1- High moisture resistance and good dielectric resistance

2- Excellent chemical resistance, abrasion resistance, moisture resistance and high temperatures up to 150 O C

缺点：

1-epoxy conformal paint is very hard and rigid and can damage PCB and its components if attempted peeling or removal. 使用危险溶剂去除涂层

2-低温性能差

3- 高固化收缩率

4-它们很难重做

L 硅树脂 (OSR) 敷形涂层：

The softest of the above two types of conformal coatings is silicone resin (OSR) conformal coatings. They are widely used in LED lamp PCBS without reducing light intensity or color change. Ideal for PCB installation at high humidity and exposure to air. Suitable for PCB with high operating temperature and high power

好处

1- 良好的耐化学性、防潮性、盐雾和高达 200 OC 的高温

2- Good flexibility makes it resistant to vibration stress on PCB from external environment.

3- 适用于高湿度的 PCB 户外应用

坏事：

1- 由于橡胶特性不耐磨

2- 可以返工，但不容易，需要特殊溶剂、长时间浸泡和像刷子或超声波浴一样搅拌

3- Low mechanical strength, weak adhesion to PCB substrate

L 聚氨酯 (PU) 敷形涂层：

适用于汽车、工业、仪器仪表和电信领域的 PCB 应用。 尤其是在航空航天领域，燃料蒸气不断地与电子设备的主体发生碰撞，从而渗透到内部并影响PCB板

好处

1- High resistance to moisture, chemicals (acid and alkali) and wear

缺点：

1-经过长时间的完全固化过程，由于其VOC含量高，在高温下容易变黄

2-像硅一样，不容易完全去除

L polyparaxylene conformal coating:

This type of coating is suitable for avionics, microelectronics, sensors, high-frequency circuits, and densely populated PCB-based components. It is applied by means of vapor deposition.

好处

1- Excellent dielectric strength

2- High resistance to moisture, solvents, extreme temperatures and acid corrosion

3- Can be applied evenly with very thin paint.

缺点：

1- Disassembly/rework is very difficult

2-成本高是最大的缺点。