How to effectively store and use solder paste in an SMT patch processing factory?

Store and use solder paste

Abstract: Solder paste in SMT processing is a solder paste with a certain viscosity and good thixotropy by mixing powdered solder powder alloy, flux, and some additives that play a role in viscosity and other functions. In the process of SMT patch processing and welding, solder paste is a key factor in quality control, so how should we better control and use solder paste? The following SZTech-SMT will give you a brief explanation.

Storage conditions

1. When the solder paste is not in use, it should be stored in the refrigerator, and its storage temperature must be within the range of 3~7°C. Please note that the solder paste cannot be frozen below 0°C.

2. There should be a dedicated thermometer in the refrigerator to detect the stored temperature every 12 hours and make a record. The thermometer needs to be checked regularly to prevent failure, and relevant records should be made.

3. When purchasing solder paste, it is necessary to paste the purchase date to distinguish different batches. According to the SMT chip processing order, it is necessary to control the use cycle of solder paste, and the inventory is generally controlled within 30 days.

4. Solder paste storage should be stored separately according to different types, batch numbers, and different manufacturers. After purchasing solder paste, it should be stored in a refrigerator, and the principle of first-in, first-out should be followed.

Prepare before use

1. Rewarming: Solder paste is usually refrigerated in a refrigerator, and the refrigeration temperature is 3~7°C. Therefore, when the solder paste is taken out of the refrigerator, its temperature is much lower than at room temperature. It is easy to open the bottle cap without “rewarming it”. The water vapor in the air is condensed and adhered to the solder paste. During reflow soldering, the water is rapidly vaporized due to strong heat, resulting in the phenomenon of “exploding tin”, producing tin beads, and even damaging components.

2. Way of returning to temperature: Without opening the bottle cap, place it at room temperature to thaw naturally, so that the temperature of the solder paste will naturally return to room temperature.

3. Rewarming time: 4-6 hours. If the unopened container has been reheated for more than 12 hours, it needs to be re-frozen in the refrigerator and then reheated for use. On the other hand, if there is any remaining solder paste after it is opened and you want to continue using it in the next round of patch processing instead of discarding it, we should seal the solder paste container again and store it in the refrigerator.

4. Stirring: The solder paste needs to be fully stirred before use, so that the flux and tin powder are evenly distributed, and various characteristics are fully utilized. Machine stirring is generally controlled within 5 minutes. The effect of stirring is judged: use a scraper to scrape up part of the solder paste, and the solder paste can slide down smoothly, which can meet the SMT chip processing requirements.

5. Before putting into patch processing and printing, if the printed PCB board with solder paste does not meet the quality requirements or there is no patch to be cleaned for more than 30 minutes, it is necessary to clean the surface of the PCB with a dust-free cloth and cleaning solution, and then blow the PCB with an air gun. No solder paste residue is allowed.

Summary of how to store solder paste

Next, I would like to remind everyone that the solder paste that has not been fully “warmed up” should not be opened for use; do not use heating to shorten the time for warming up; when the solder paste is taken out of the refrigerator, we will post it. Use the label on the label, and fill in the thawing start time, which will help us to control it more effectively; when the solder paste solidifies, the surface will form a thin shell and cannot be used;

The above is how to store and use solder paste shared by SZTech-SMT for you. I hope it will be helpful to you. To learn more about SMT patch processing, please visit www.sztech-smt.com

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