1. What are the characteristics of solder paste?

Viscosity, fluidity, thixotropy, melting point is usually lead 183, lead-free 217, etc.

2. The welding process of solder paste components?

It can be divided into four stages: heating, constant temperature, reflux, and cooling

Temperature rise: PCB with good printed patch enters reflow soldering and slowly heats up from room temperature, with the heating rate controlled at 1-3 ℃/S.

Constant temperature: keep the flux in the solder paste at a stable temperature and volatilize it appropriately.

Reflow: At this point, the temperature rises to * high, the solder paste liquefies, and an alloy is formed between the PCB pad and the part solder end, completing the welding process

Next, the time is around 60s, determined by the solder paste.

Cooling: Cooling the welded plate can be achieved by controlling the cooling speed well, such as ROHS 6-7 ℃/S.

3. How to optimize process parameters? Optimization of profile curves?

Generally, it takes three steps: preset, measurement, and adjustment to obtain the optimal parameters.

Taking the furnace temperature curve as an example, the travel speed and temperature of reflow soldering soldering should be preset according to the type of solder paste, PCB thickness, etc

Measure the actual temperature curve of the PCB board using a furnace temperature tester, and then refer to past experience and

The routine process of solder paste welding requires analysis, repeated adjustment and verification of the preset temperature and speed,

Then obtain a suitable curve file.

4. What are the effects of solder paste, process parameters, and machine equipment on printing solder paste? How to improve?

Firstly, the formability, thixotropy and fluidity of solder paste may occur due to its component ratio, particle size or non-standard use

Poor characteristics such as collapse, short circuit, and lack of tin during printing may result.

Process parameters such as printing pressure, scraper speed, scraper angle, etc. can cause insufficient tin content, pinching, irregular forming, or

Poor soldering and other defects after soldering.

The hardware mainly focuses on scraper hardness, steel mesh tension, opening size, opening shape, surface roughness, steel mesh thickness, and

There are many factors that determine the quality of solder paste printing due to poor printing caused by the support and fixation of the PCB by the printing machine.

In actual production, based on the actual problems, analyze the causes of the actual defects and mediate them to the best.