焊接面罩，也称为阻焊面罩，是一层薄薄的聚合物，用于 PCB板 以防止焊点形成桥接。 焊接面罩还可以防止氧化，适用于 PCB 板上的铜迹线。

What is PCB solder resistance type? The PCB welding mask acts as a protective coating on the copper trace line to prevent rust and prevent solder from forming Bridges that lead to short circuits. PCB焊接面罩主要有4种类型——环氧树脂液体、液体可照相、干膜可照相以及顶部和底部掩模。

四种电焊面罩

焊接面罩的制造和材料各不相同。 如何使用以及使用哪种焊接面罩取决于应用。

顶部和底部侧盖

顶部和底部焊接掩模电子工程师经常使用它来识别绿色阻焊层中的开口。 该层是通过环氧树脂或薄膜技术预先添加的。 然后使用与掩模对准的开口将元件引脚焊接到电路板上。

The conductive trace pattern on the top of the circuit board is called the top trace. 与顶面罩类似，底面罩用于电路板的反面。

环氧树脂液体阻焊层

Epoxy resins are the cheapest alternative to welding masks. Epoxy is a polymer that is screen printed on a PCB. 丝网印刷是一种使用织物网来支撑油墨阻挡图案的印刷工艺。 The grid allows identification of open areas for ink transfer. In the final step of the process, heat curing is used.

液体光学成像阻焊层

液体光导掩模，也称为LPI，实际上是两种不同液体的混合物。 Liquid components are mixed prior to application to ensure a longer shelf life. It is also one of the more economical of the four different PCB solder resistance types.

LPI 可用于丝网印刷、丝网绘画或喷涂应用。 The mask is a mixture of different solvents and polymers. 结果，可以提取粘附到目标区域表面的薄涂层。 该掩模用于焊接掩模，但 PCB 不需要任何当今常见的最终电镀涂层。

与旧的环氧树脂油墨相比，LPI 对紫外线很敏感。 面板需要用面罩覆盖。 经过短暂的“固化周期”后，电路板会使用光刻或紫外激光暴露在紫外光下。

Before applying the mask, the panel should be cleaned and free of oxidization. 这是在特殊化学溶液的帮助下完成的。 这也可以使用氧化铝溶液或用悬浮的浮石擦洗面板来完成。

One of the most common ways to expose panel surfaces to UV is by using contact printers and film tools. The top and bottom sheets of the film are printed with an emulsion to block the area to be welded. Use the tools on the printer to fix the production panel and film in place. The panels were then simultaneously exposed to an ULTRAVIOLET light source.

另一种技术使用激光来创建直接图像。 But in this technique, no film or tools are needed because the laser is controlled using a reference mark on the panel’s copper template.

LPI 遮罩有多种颜色可供选择，包括绿色（哑光或半光）、白色、蓝色、红色、黄色、黑色等。 LED 行业和电子行业中的激光应用正在鼓励制造商和设计师开发更强的白色和黑色材料。

干膜光成像阻焊层

A dry film photoimagable welding mask is used, and vacuum lamination is used. 然后对干膜进行曝光和显影。 After the film is developed, openings are positioned to produce patterns. 在此之后，元件被焊接到钎焊垫上。 然后使用电化学工艺将铜层压到电路板上。

铜在孔中和走线区域中分层。 Tin was eventually used to help protect copper circuits. In the final step, the membrane is removed and the etching mark is exposed. 该方法还使用热固化。

Dry film welding masks are commonly used for high-density patch boards. 结果，它不会倒入通孔中。 These are some of the positives of using a dry film welding mask.

决定使用哪种焊接面罩取决于多种因素——包括 PCB 的物理尺寸、要使用的最终应用、孔、要使用的组件、导体、表面布局等。

大多数现代 PCB 设计都可以获得可光成像的阻焊膜。 Therefore, it is either LPI or dry film resistance film. The surface layout of the board will help you determine your final choice. If the surface topography is not uniform, the LPI mask is preferred. If a dry film is used on uneven terrain, gas may be trapped in the space formed between the film and the surface. Therefore, LPI is more suitable here.

但是，使用 LPI 也有缺点。 Its comprehensiveness is not uniform. You can also get different finishes on the mask layer, each with its own application. For example, in cases where solder reflow is used, the matte finish will reduce solder balls.

Build solder masks into your design

Building a solder resist film into your design is indispensable to ensure the mask application is at the optimal level. When designing a circuit board, the welding mask should have its own layer in the Gerber file. In general, it is recommended to use a 2mm border around the function in case the mask is not fully centered. 您还应该在焊盘之间留出至少 8 毫米的距离，以确保不会形成桥接。

Thickness of welding mask

Thickness Welding mask will depend on the thickness of the copper trace on the board. 一般来说，最好使用 0.5mm 的焊接面罩来掩盖走线。 If you are using liquid masks, you must have different thicknesses for different features. Empty laminate areas may have a thickness of 0.8-1.2mm, while areas with complex features such as knees will have thin extensions (about 0.3mm).

结论

总之，焊接面罩设计对应用功能有严重影响。 它在防止锈蚀和焊接桥梁方面起着至关重要的作用，这会导致短路。 因此，您的决定需要考虑本文中提到的不同因素。 希望这篇文章可以帮助您更好地了解PCB电阻膜的TYPE。 如果您有任何问题，或者只是需要联系我们，我们随时乐意为您提供帮助。