What is solder mask opening?

Table of Contents:

  1. How to define solder mask?
  2. What are the process requirements for solder mask?
  3. What are the process of solder mask?
  4. How to understand pcb solder mask opening?
  5. Why PCB window solder mask?

How to define solder mask?

The solder mask refers to the green oil on the printed circuit board. In fact, this solder mask layer uses negative output, so after the shape of the solder mask layer is mapped on the board, it is not green oil solder mask, but the copper skin is exposed.

What are the process requirements for solder mask?

The role of the solder mask in controlling soldering defects during the reflow soldering process is important. When designing a PCB, the designer should try to minimize the space or air gap around the pad features.

Although many process engineers prefer solder masks to separate all pad features on the board, the lead spacing and pad size of densely spaced components will require special considerations. Although solder mask openings or windows that are not partitioned on the four sides of the qfp may be acceptable, it may be more difficult to control the tin bridge between the component pins. For the BGA solder mask, many companies provide a solder mask that does not contact the pads but covers any features between the pads to prevent tin bridges. Most surface-mount PCBs are covered with solder masks, but if the thickness of the solder mask is greater than 0.04mm, it may affect the application of solder paste. Surface-mount PCBs, especially those using dense-pitch components, All require a low-profile photosensitive solder resist.


What are the process of solder mask?

Solder mask materials must be used either by a liquid wet process or a dry film stack. Dry film solder mask material is supplied in a thickness of 0.07-0.1mm (0.03-0.04 ″) and may be suitable for some surface mount products, but this material is not recommended for close-pitch applications. Generally, solder mask openings should The pads are 0.15mm (0.006 ″) larger. This allows 0.07mm (0.003 ″) clearance on all sides of the pad. Low-profile liquid photosensitive solder mask materials are economical and are usually specified for surface mount applications, providing accurate feature sizes and clearances.

How to understand pcb solder mask opening?

The solder mask opening window refers to the size of the part where the copper needs to be exposed, that is, the size of the part that is not covered with ink. Too small cover line distance will cause exposed lines during production.

Why PCB window solder mask?

Aperture opening window: Because many customers do not need ink plug holes, if the window is not opened, the ink will enter the holes. If the large holes are blocked with ink, the customer cannot press the key(This is for the small holes).In addition, if it is a gold plate, it must be opened.

When PCB soldering, the window will be opened with PAD of the solder paste layer (customers need soldering, surface treatment).


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