How to judge whether the printed circuit board design uses matte finish?

When creating the best circuit board design, one of the necessary factors to consider is the solder resist layer and whether to use matte finish or gloss mask of the final product. In general, most designers do not specify their preferences, and the final decision is left to them pcb manufacturer. Most manufacturers default to glossy surface finish, which is the most popular choice of the two.

When discussing welding standards, these two types have no different requirements. Qualification and performance of ipc-sm-840c permanent flux, including use information. The purpose of this specification is to promote suppliers to evaluate welding layers using standard circuit board systems and to help designers, manufacturers and users jointly certify the technology for producing circuit boards.

The specific difference between the two types is aesthetics. Photoresist flux has light reflection and light color, while matte has no luster and looks very dark. Non photoresist flux also tends to be softer (porous), while gloss has a hard shell finish. In the manufacturing of printed circuit board, there is no difference in process. If there is, the cost difference is very small.

Matte finishes may be easier to scratch because of soft finishes, but scratches are more obvious on shiny finishes. Matte is also easier to show cosmetics and white fog / residues. Glossy finish boards do not show this; However, due to the high reflectivity, the glossy solder mask may cause visual system problems during assembly. When using glossy masks, mask removal around the reference point plays an important role in the visual system.

Many reports from contract manufacturers (CM) show that matte finishes are difficult to form solder balls. In case of doubt, CM listed the mask model as the specific cause of flux solder ball. Solder balls usually exist at the bottom of the printed circuit board. The use of unclean low residue welding will attract more attention.

Over the years, many possible reasons have been put forward after the formation of solder balls. One of the reasons is:

(1) Glass transition temperature.

(2) Surface energy.

(3) Hardness.

(4) Flux type.

(5) There is moisture.

(6) Surface roughness.

At present, although surface roughness has always been a specific factor in the production of solder balls, its exact mechanism has not been fully understood. According to the technical report of vantico (formerly known as Ciba Specialty chemicals), molten solder on rough (matte) surface is different from molten solder on smooth surface - mask and laminate for various PCB solder. On the rough surface, the molten solder produces a convex lunar surface, and on the smooth surface, the molten solder produces a concave lunar surface. Convex and concave lunar surfaces reduce the attachment area of the solder ball, so the solder ball will not adhere to the matte surface like a smooth surface.

Many studies on gloss are related to welding defects. It is found that the gloss of photo imaging will affect the number of welding defects in the wave soldering process of circuit board. These welding defects (solder ball, solder short circuit, welding bridge) are directly proportional to the gloss. With the decrease of gloss, the reduction rate of solder ball level is faster than the number of welding short circuits and bridges. In other words, in order to reduce or eliminate the welding short circuit, the required gloss is lower than that required to reduce the solder ball.