Why does the solder paste need to be stirred, thawed and returned to temperature before SMT chip processing?

Friends who work in SMT chip factories all know that the solder paste used in SMT needs to be refrigerated and stored in a freezer (2-8°C). Its purpose is to slow down the reaction speed of flux and tin powder, ensure the welding quality of components and PCB, and thereby prolong the quality of effective welding. So why does the solder paste need to be stirred and warmed before SMT chip processing? Maybe many friends don’t know the real reason.

1. The first step of solder paste before SMT chip processing is to rewarm. The so-called rewarming is also what we often call thawing. The solder paste is thawed by self-heating at normal temperature, rather than through other heating methods. This One thing needs special attention. If the solder paste that has not been thawed is used, the water vapor in the air will easily condense and adhere to the tin paddle. During the reflow soldering process, the water will be heated and vaporized quickly, which will easily cause tin explosion and eventually produce tin beads.

1. The purpose of thawing and rewarming: it can make the flux and tin powder evenly distributed, so as to give full play to the various characteristics of the solder paste; the viscosity and activity of the refrigerated solder paste are different from those at room temperature. The purpose of warming is also to allow the solder paste to fully restore its original viscosity and activity;

2. Method of thawing and warming up: Take the solder paste out of the refrigerator and place it at a standard room temperature of 22-28°C for thawing at room temperature. The solder paste in the original package must be warmed up for at least 4 hours. Secondary use of solder paste must be thawed within 3-4 hours;

2. The next step is to stir the solder paste; because there are various metal components and flux components in the solder paste, and due to the different densities of each substance, metals with high density will sink during storage, so after the solder paste is thawed and warmed up, It must be stirred before use.

1. Purpose of stirring: The purpose of stirring is to stir the internal tin powder particles and soldering flux materials evenly and increase the fluidity and plasticity. The fluidity and plasticity of the stirred solder paste will be greatly improved.

2. Mixing method: There are two methods of mixing: manual mixing and machine mixing; mixing time: manual mixing clockwise for about 5 minutes, and machine mixing for 3 minutes. The solder paste should not be stirred for too long. Too long may cause the solder paste to be higher than the operating room temperature and flow during printing. To determine the mixing effect, you can use a scraper to scrape up part of the solder paste. When the scraper is tilted, if the solder paste can fall smoothly and uninterrupted, the stirring requirements are met.

solder paste is a very critical auxiliary material in SMT patches, and it is also an important process control point that affects the welding quality of SMT patch processing. Solder paste is very important no matter which step it is used. Therefore, we must follow each of the above steps in actual SMT patch applications

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top