What is the meaning of the pcb solder mask opening window?

What is the meaning of the pcb solder mask opening window?

Solder mask concept

The solder mask is the soldermask, which refers to the part of the printed circuit board that is to be greened. In fact, this solder mask uses the negative output, so after the shape of the solder mask is mapped to the board, it is not the green oil solder mask, but the copper skin is exposed.

Process requirements for solder mask

The role of the solder mask in controlling soldering defects during the reflow soldering process is important, and PCB designers should minimize the spacing or air gap around the pad features.

While many process engineers prefer that the solder mask separate all pad features on the board, the pin spacing and pad size of the fine pitch components will require special consideration. Although solder mask openings or windows that are not partitioned on the four sides of qfp may be acceptable, it may be more difficult to control the tin bridge between the component leads. For bga solder masks, many companies offer a solder mask that does not touch the pads but covers any features between the pads to prevent solder bridges. Most surface mount PCBs are covered with a solder mask, but the solder mask coating, if thicker than 0.04 mm ("), may affect the application of solder paste. Surface mount PCBs, especially those that use fine pitch components, A low profile photoresist layer is required.

Solder mask manufacturing process

The solder mask material must be used by a liquid wet process or a dry film laminate. The dry film solder resist is supplied in a thickness of 0.07-0.1mm (0.03-0.04") and is suitable for some surface mount products, but this material is not recommended for close pitch applications. Few companies offer thin enough to meet Dry film with a standard pitch, but several companies can provide liquid photoresist. Typically, the solder mask opening should be 0.15 mm (0.006") larger than the pad. This allows a gap of 0.07 mm (0.003") across all sides of the pad. Low profile liquid photo solder mask materials are economical and are typically specified for surface mount applications, providing precise feature size and clearance.

Understanding of pcb solder mask opening window

The solder mask open window refers to the size of the portion where the solder is required to expose the copper, that is, the size of the portion where the ink is not covered, and the cover line refers to the size and the amount of the solder resist oil covering the line portion. If the cover line distance is too small, the line will be exposed during the production process.

PCB solder mask opening window

1. Aperture opening: It is because there are many customers who do not need ink plug holes. If the window is not opened, the ink will enter the hole. (This is for small holes.) If the large hole is filled with ink, the customer cannot press the button. In addition, if it is a gold plate, you must open the window.

2.PAD (that is, copper) window opening: customers need welding, surface treatment (gold / spray tin, etc.).