Depth analysis: What are the factors that affect the thickness of SMT press solder paste printing?
In the solder paste printing machine, sometimes the printed solder paste is very thin, which causes the product to fall off due to too little solder paste after the furnace is finished. So how is this phenomenon caused? Below I will analyze some specific reasons for everyone.
First, the quality of the steel plate — stencil printing is contact printing, so the stencil thickness and opening size determine the amount of solder paste printing, too much solder paste will produce bridging, too little solder paste will occur solder deficiency or solder joint, template The shape of the opening and the smoothness of the opening also affect the quality of the release. The template opening must have the bell mouth down, otherwise the solder paste will be taken from the chamfered corner of the bell when the mold is released. DEK accessories
Second, the printing process parameters — solder paste is a thixotropic fluid, with viscosity, when the scraper moves forward at a certain speed and angle, push the solder paste to roll in front of the scraper, the need to inject solder paste into the mesh or leak hole The pressure, the viscous friction of the solder paste causes the solder paste to shear at the intersection of the squeegee and the stencil, and the shear force reduces the viscosity of the solder paste, which facilitates the smooth injection of the solder paste into the mesh. There is a certain constraint between the speed of the blade, the pressure of the blade, the angle of the blade and the stencil, and the viscosity of the solder paste. Therefore, only by properly controlling these parameters can the printing quality of the solder paste be ensured.
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Third, contact printing blade pressure:
1 blade pressure 10~20 depends on the size of the press or template installation;
2 The blade pressure should be sufficient to scrape the template;
3 The blade pressure is too high, which may result in:
- Speed up the wear of the template;
2, printing causes solder paste pattern adhesion;
- The solder paste is hollow;
The solder paste is pressed out from the reverse side of the template to cause the solder ball.
Fourth, the contact printing blade speed:
1 fine pitch (12-20mil0.5-1.5 inches / sec (13-38mm /
2 custom pitch (20-50mil1.5-4.5 inches / sec (38-115mm /
3 solder paste viscosity will have a certain impact on the speed of the scraper
4 reduce the speed of the blade will increase the thickness of the solder paste printing
5 template thickness increases, scraper speed should be reduced accordingly
6 printing too fast is easy to cause insufficient solder paste
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