Solder application process and precautions：solder paste

Solder Paste

◇Solder application process and precautions：solder bar

◇Precautions for using solder wire, solder sheets, and solder balls

Solder Paste Storage

 

 

① The placement requirements for solder paste in the refrigerator are as follows:

• Lead-containing solder paste and lead-free solder paste must be stored separately in different refrigerators.
• Solder pastes with different production dates must be stored separately, while solder pastes of the same batch should be stored together.

 

② Temperature control requirements for the auxiliary material storage refrigerator: The storage temperature for solder paste is 0~10℃. The refrigerator temperature is generally set to 5℃, and the alarm temperature is generally set to 2~8℃.

③ If the refrigerator temperature is not within the 2~8℃ range after the temperature has stabilized, the stencil room administrator must immediately take corrective measures to adjust the refrigerator temperature to within the set temperature range. If the refrigerator temperature cannot be adjusted to within the set temperature range within 20 minutes, the solder paste in the refrigerator must be transferred to a nearby refrigerator with a normal storage temperature.

Solder Paste Usage

 

① After receiving the solder paste, open the container lid only when needed. After opening, stir the solder paste manually with a spatula for 2-3 minutes (stirring in the same direction) to ensure the components are evenly distributed. When adding solder paste, follow the principle of "small amounts multiple times" (2-3 times per container). The ideal amount is when the solder paste forms a roll with a height of 10-20mm on the stencil, ensuring it rolls rather than slides on the steel plate. After adding, immediately seal the container with the lid and close the printing machine's cover. Avoid prolonged exposure of the solder paste to air, as this can cause flux evaporation or moisture absorption, affecting its performance.

② Solder Paste Printing.

• Operators must wear appropriate personal protective equipment (such as anti-static gloves) when handling solder paste to avoid direct contact with the skin. If contact occurs with the mouth, nose, or skin, immediately rinse with clean water; if any adverse reaction occurs, seek medical attention immediately; if it gets into the eyes, seek medical attention immediately.
• When manually wiping the stencil, the solder paste on both sides of the squeegee must be scraped back into the printing area.
• Stencils and squeegees used online must be sent to the stencil cleaning room every 12 hours for cleaning. If the solder paste type is changed, both the stencil and squeegee must be cleaned.
• The squeegee must be kept clean. After each addition of solder paste, the squeegee should be wiped clean with stencil paper to prevent solder paste residue and repeated contamination. The squeegee should not be made of metal to prevent deformation of the tin powder in the solder paste during operation.
• The designated operator must adjust the printing parameters (including the demolding gap between the stencil and the PCB, squeegee pressure and speed, wiping frequency, etc.) and ensure the printing effect. After solder paste printing, the solder paste printing quality must be checked with a 3-5x magnifying glass. Only after the PQC (Process Quality Control) determines that the solder paste printing is qualified can continuous mass production begin. Afterward, random checks must be performed using a 3-5x magnifying glass.
• The operator must randomly check the printing effect four times per hour (recommended: check interval of 10-15 minutes). Manual stencil wiping must be performed strictly according to the "SMT Solder Paste Printing Process Guidance Card," and the bottom of the stencil should be checked for hard solder lumps, clogged mesh holes, and stencil deformation. Any abnormalities should be reported immediately and corrective measures taken.
• If stencil holes are clogged, clean the stencil with an air gun and stencil paper, and carefully check the printing quality of the next two consecutive boards.
• PCBs with printed solder paste must have components mounted and go through the reflow soldering furnace within 1 hour; otherwise, it is considered defective printing, and the PCB should be cleaned according to the prescribed method. If the machine is stopped for more than 1 hour, the solder paste on the stencil must be returned to the bottle and sealed. 

Solder Paste Recycling

• ① Solder paste that has been continuously used on the stencil for less than 8 hours can be bottled separately when production ends and transferred to the SMT stencil room as soon as possible. The SMT stencil room administrator will fill out the "Solder Paste Return Tracking Form" 500001061600-Q-3, record the tracking information, and store it in a constant-temperature refrigerator. It should be prioritized for use on simple boards.
• ② Solder paste that has remained in the bottle and has been opened for less than 24 hours, and is no longer needed by the user, should be transferred to the SMT stencil room as soon as possible. The SMT stencil room administrator will fill out the "Solder Paste Return Tracking Form" 500001061600-Q-3, recording the tracking information,so that it can be prioritized for transfer to other production lines.
• ③ If solder paste that has remained in the bottle and has been opened for less than 24 hours needs to be recycled, the recycling storage time should be indicated in the "Return Storage Time After Opening" section on the solder paste bottle cap label. It is recommended to use it only for simple boards.
• ④ Recycled solder paste should be stored separately from other solder paste in the constant-temperature refrigerator, and the words "Recycled for Reuse" should be noted in the "Other Instructions" section of the label for differentiation. All opened solder paste can only be recycled once.