The Difference and Role of PCB Paste Mask and Solder Mask

The Difference and Role of PCB Paste Mask and Solder Mask

 

Introduction to solder mask

 

The solder mask is the soldermask, which refers to the part of the 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. Usually in order to increase the thickness of the copper skin, the solder mask is used to scribe the green oil, and then tin is added to increase the thickness of the copper wire.

PCB solder mask

 

Solder mask requirements

 

Solder masks are important in controlling soldering defects in reflow soldering, and PCB designers should minimize the spacing or air gap around the pads.

 

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 solder paste application. Surface mount PCBs, especially those that use fine pitch components, require a low photoresist layer.

 

Production

 

The solder mask material must be used by a liquid wet process or a dry film laminate. The dry film solder mask is supplied in a thickness of 0.07-0. 1 mm and is suitable for some surface mount products, but this material is not recommended for close pitch applications. Few companies offer thin films that are thin enough to meet the fine pitch criteria, but several companies offer liquid photo solder masks. Typically, the solder mask opening should be 0.15 mm larger than the pad. This allows a gap of 0.07 mm on the side 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.

Stencil

 

 

Introduction to the paste mask

 

The paste mask is used for the chip package and corresponds to the chip component pad. In the SMT processing, a steel plate is usually used to punch the hole on the PCB corresponding to the component pad, and then the solder paste is applied on the steel plate. When the PCB is under the steel plate, the solder paste leaks, which is just on each pad. Solder can be soldered, so usually the solder mask cannot be larger than the actual pad size, preferably less than or equal to the actual pad size.

 

The required level and surface-mount components are almost the same, mainly requiring the following elements:

 

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: the middle layer

 

Solder mask and paste mask

 

The solder mask is mainly to prevent the PCB copper foil from being directly exposed to the air for protection.

 

The soldering layer is used to make the steel mesh for the steel mesh factory, and the steel mesh can accurately place the solder paste on the soldering pad to be soldered when the tin is applied.

The solder mask layer

 

 

The difference between paste mask and solder mask

 

Both layers are used for soldering on the tin, but not for a tin, or a green oil, instead:

1. The solder resist layer means to open the window on the whole piece of solder resist green oil, the purpose is to allow welding;

2. By default, green oil should be applied to areas where there is no solder mask;

3. the solder layer is used for chip package