PCB Technical - PCB process How to print solder paste on the circuit board

PCB process How to print solder paste on the circuit board

Printing the solder paste on the circuit board and then connecting the electronic parts to the PCBA board through a reflow oven is the most common method used by circuit board manufacturers today. The printing of solder paste is actually a bit like painting on a wall. The difference is that in order to apply the solder paste to a certain position and control the amount of solder paste more accurately, a more precise special steel plate (stencil) must be used. To control the printing of solder paste.

▲Before solder paste printing. There is only a gold-plated layer on the circuit board.

▲After the solder paste is printed, the solder paste here is designed in the shape of "Tian" to prevent the solder paste from being too concentrated in the center after melting.

Solder paste printing is the basis for the quality of the solder on the circuit board, and the position of the solder paste and the amount of solder are even more critical. It is often seen that the solder paste is not printed well, causing solder short and solder empty, etc. There was a problem. However, if you really want to print the solder paste, you have to consider the following factors:

Squeegee: Solder paste printing should choose the appropriate squeegee according to the characteristics of different solder paste or red glue. At present, the squeegee used for solder paste printing is made of stainless steel.
Scraper angle: The angle at which the squeegee scrapes the solder paste, generally between 45 and 60°.

Squeegee pressure: The pressure of the squeegee affects the volume of solder paste. In principle, under other conditions unchanged, the greater the pressure of the squeegee, the less the amount of solder paste will be. Because of the high pressure, it is equivalent to compressing the gap between the steel plate and the circuit board.

Squeegee speed: The speed of the squeegee will also directly affect the shape of the solder paste printing and the amount of solder paste, and it will directly affect the quality of the solder printing. Generally, the speed of the squeegee is set between 20 and 80mm/s. In principle, the speed of the squeegee must match the viscosity of the solder paste. The better the fluidity of the solder paste, the faster the squeegee speed, otherwise it will easily seep. In general, the faster the squeegee, the smaller the amount of solder paste.

The demolding speed of the steel plate: If the demolding speed is too fast, it is easy to cause the phenomenon of wire drawing or sharpening of the solder paste, which may affect the effect of the placement.

Do you use a vacuum block? The vacuum seat can help the circuit board to be smoothly attached to a fixed position and strengthen the tightness of the steel plate and the circuit board. Sometimes only a small quantity of products produced at a time can use a universal thimble/top block instead of a vacuum block.

Is the circuit board deformed (warapge)? A deformed circuit board will cause the solder paste to be printed unevenly, and in most cases will cause a short circuit.

Steel plate opening (stencil aperture). The opening of the steel plate directly affects the quality of solder paste printing, which requires a special chapter.