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Pcb maker through hole reflow solder paste

 

For the PCB maker, the key problem of through-hole reflow soldering technology is that the amount of solder paste required for via solder joints is larger than that required for surface mount solder joints, and the solder paste printing method using the conventional reflow process. It is not possible to apply a proper amount of solder paste to the via components and surface mount components at the same time. The solder amount of the via solder joints is usually insufficient, so the solder joint strength will be lowered. The PCB maker can complete printing in the following two different processes.

(1) One time printing process.

In order to solve the problem of different solder paste requirements for through-hole components and surface mount components, the PCB maker uses a local thickening template for  printing at one time.

The PCB maker uses a locally thickened stencil to use a manual solder paste, while the squeegee uses a rubber squeegee. The printing process is consistent with traditional SMT printing. Generally, the thickness of the parameter A=0.15mm and B=0.35mm in the local thickening template can meet the requirements of the amount of solder joint paste soldering in the through-hole reflow soldering. Since the local thickening template uses a rubber scraper, the rubber scraper deforms greatly under pressure, so that there is a defect in the solder paste pattern after printing.

 

(2) Secondary printing process.

One printing process uses a local thickening stencil and a rubber squeegee to complete the printing. However, for some mixed circuit boards with high lead density and extremely small lead diameter,if PCB Maker using local thickening stencil process to print solder paste at one time cannot meet the printing quality. The secondary printed solder paste process is required. Firstly, the PCB maker usually uses a 0.15mm thick first-level stencil to print the surface-mount component solder paste, and then uses a second-level stencil of 0.3-0.4mm thickness to print the solder paste of the via-hole component. In order to prevent the back surface of the second printing template from being etched to the surface mounting pad, a groove with a depth of 0.2 mm is etched.

 

Regardless of whether the PCB maker uses a single printing process or a secondary printing process, when the quality of the solder used for through-hole reflow soldering is 80% of the solder quality used for wave soldering, the solder joints strength compared with that during wave soldering is comparable, but if the solder quality of the via plug components is below this critical amount, the solder joint strength formed is not up to standard. 80% is defined as the critical amount of through-hole reflow solder. Whether using a single printing process or a secondary printing process, the amount of solder used for via reflow is greater than this critical amount.

 

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