In the solder paste
printing process, the thickness of the solder paste is relatively thin, which will cause less tin and false soldering of components. How to solve such a problem? How to adjust the printing press? How to increase tin thickness?
The thickness of the solder paste is determined by the stencil. The 0.15mm stencil is controlled at about 0.13mm-0.18mm. The thickness of the stencil does not meet the requirements (too thin) choose a stencil with an appropriate thickness. 2. The pressure of the scraper is too high to adjust the pressure of the scraper. 3. The printing speed is too fast to slow down the printing speed or increase the number of printing times. 4. Poor fluidity of solder paste Choose solder paste with suitable particle size and viscosity.
The direct and effective way is to increase the thickness of the steel mesh; this will be easier to control, and the thickness of the thicker solder paste is better for BGAopen, but special care must be taken in the selection of thickness increase, and the width-thickness ratio in the stencil opening design principle> 1.5, and the area ratio is greater than 0.66. On this basis, referring to the welding quality design in the case of opening holes before, it can be concluded that the thicker steel mesh needs to be opened to avoid bridging. A good stencil opening design can avoid many bad occurrences, and can also avoid being blamed by the boss. It will be easier to get the appreciation of the boss, the reason is very simple but very practical.
Emergency measures when the stencil remains unchanged: Adjustment of the printing machine: increase the plate thickness setting/increase the printing spacing/reduce the pressure of the scraper. Adjustment of the stencil: dog skin plaster type-paste high temperature tape or stencil sticker on the back of the stencil- This should be well controlled. The method and thickness of the paste means that several layers are pasted to complete the control of the printing process.