Introduction to Solder Mask
The resistance pad is soldermask, which refers to the part of the circuit board to be painted with green oil. In fact, this solder mask uses a negative output, so after the shape of the solder mask is mapped to the board, the solder mask is not painted with green oil, but the copper skin is exposed. Usually in order to increase the thickness of the copper skin, the solder mask is used to scribe lines to remove the green oil, and then tin is added to increase the thickness of the copper wire.
Requirements for solder mask
The solder mask is very important in controlling soldering defects in reflow soldering. PCB designers should minimize the spacing or air gaps around the pads.
Although many process engineers would rather separate all pad features on the board with a solder mask, the pin spacing and pad size of fine-pitch components will require special consideration. Although solder mask openings or windows that are not zoned on the four sides of the qfp may be acceptable, it may be more difficult to control solder bridges between component pins. For the solder mask of bga, many companies provide 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 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 fine-pitch components, require a low photosensitive solder mask.
Work production
Solder mask materials must be used through liquid wet process or dry film lamination. Dry film solder mask materials are supplied in a thickness of 0.07-0.1mm, which can be suitable for some surface mount products, but this material is not recommended for close-pitch applications. Few companies provide dry films that are thin enough to meet the fine pitch standards, but there are a few companies that can provide liquid photosensitive solder mask materials. Generally, the solder mask opening should be 0.15mm larger than the pad. This allows a gap of 0.07mm on the edge of the pad. Low-profile liquid photosensitive solder mask materials are economical and are usually specified for surface mount applications to provide precise feature sizes and gaps.
Introduction to soldering layer
The soldering layer is used for SMD packaging and corresponds to the pads of SMD components. In SMT processing, a steel plate is usually used, and the PCB corresponding to the component pads is punched, and then solder paste is placed on the steel plate. When the PCB is under the steel plate, the solder paste leaks, and it is just on each pad It can be stained with solder, so usually the solder mask should not be larger than the actual pad size, preferably less than or equal to the actual pad size.
The level required is almost the same as that of surface mount components, and the main elements are as follows:
1. BeginLayer: ThermalRelief and AnTIPad are 0.5mm larger than the actual size of the regular pad
2. EndLayer: ThermalRelief and AnTIPad are 0.5mm larger than the actual size of the regular pad
3. DEFAULTINTERNAL: middle layer
The role of solder mask and flux layer
The solder mask layer mainly prevents the copper foil of the circuit board from being directly exposed to the air and plays a protective role.
The soldering layer is used to make steel mesh for the steel mesh factory, and the steel mesh can accurately put the solder paste on the patch pads that need to be soldered when tinning.
The difference between PCB soldering layer and solder mask
Both layers are used for soldering. It does not mean that one is soldered and the other is green oil; but:
1. The solder mask layer means to open a window on the green oil of the whole solder mask, the purpose is to allow welding;
2. By default, the area without solder mask must be painted with green oil;
3. The soldering layer is used for SMD packaging.