What are the main reasons that affect the quality of solder paste printing in the SMT process?

There are many factors that affect the printing quality, such as the quality of solder paste and the quality of the template.SMTPrinting process parameters, environmental temperature, humidity, equipment precision, etc. Moreover, printing solder paste is a dynamic process. Therefore, it is very necessary to establish a complete set of printing process control documents. Choosing the correct solder paste and steel mesh, and combining them with the most suitable printing machine parameter Settings, can make the entire printing process more stable, controllable and standardized. The following is provided by JJYSolder pasteLet the manufacturer introduce roughly what the reasons are:

Factors affecting solder paste viscosity:

1.  The influence of alloy powder content in solder paste on viscosity - The increase of alloy powder in solder paste leads to an increase in viscosity;

2.  The influence of the particle size of solder paste alloy powder on viscosity - Viscosity decreases as the particle size increases;

Ø  Fine particle solder paste has better printability, especially for high-density and narrow-spacing products. Due to the small opening size of the steel mesh, small particle alloy powder must be used; otherwise, it will affect the printing demolding.

Ø  The advantages of small-particle alloy powder: Good printability and high clarity of printed graphics.

Ø  The disadvantages of small-particle alloy powder: It is prone to edge collapse and those with a large surface area are easily oxidized.

3.  The influence of temperature on the viscosity of solder paste: As temperature rises, viscosity decreases. The optimal ambient temperature for printing is23±3℃;

4.  The influence of shear rate on the viscosity of solder paste: As the shear rate increases, the viscosity decreases. 

The expiration date of solder paste and its storage and usage environment:

Ø  Generally, when the solder paste is unopened,0-10℃It can be saved under certain conditions6After opening, it should be used up as soon as possible; 

Ø  The application environment of solder paste is: requiredSMTThe temperature of the room is20-26℃Humidity is40-60%;

Ø  The storage time of unopened solder paste under environmental temperature and humidity conditions≤48Hours;

Ø  The storage time of solder paste under environmental temperature and humidity conditions after opening the lid≤18Hours;

Ø  The usage time on the steel mesh≤12Hours;

Ø  The time that solder paste stays on the line after printing≤2Hours;

Ø  The time from opening the can to reflow soldering≤18Hours.

Solder paste printing is guaranteedSMTThe key process of surface mount technology (SMT) processing quality. According to statistics, under the premise of ensuring the design specifications of printed circuit boards, components and the quality of printed circuit boards, approximately60% ~ 709%The quality problem is caused bySMTCaused by the surface mount technology (SMT) processing and printing process.SMTThe amount of solder paste used in surface mount processing should be uniform and consistent. The solder paste should be clear and adjacent patterns should not stick together as much as possible. The solder paste pattern and the pad pattern should be consistent, and misalignment should be avoided as much as possible.

Under normal circumstances, the amount of solder paste per unit area on the pad should be approximately0.8 mg/mm3For the component of the piece spacing, and it should be approximately0.5mgmm2. Brush onSMTThe solder paste on the surface mount processing substrate can be allowed to have a certain deviation compared with the expected weight value. As for the area of solder paste covering each pad, it should be75%That's all. When using the no-cleaning technology, it is required that the solder paste be completely located on the solder pad, and the lead-free solder paste fully covers the solder pad.

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