Solder paste tin splattering causes and solutions

Solder paste soldering tin splattering refers to the soldering process, high temperature soldering iron tip contact solder paste, solder paste instantly produce a violent reaction, issued by the explosion sound and splattered small tin beads of the phenomenon. The following are the main reasons for tin splattering and solutions:

I. Main causes of tin splattering

Material moisture

Solder or PCB moisture: solder paste, solder wire or PCB board if not properly preserved, easy to absorb moisture in the air. Soldering, moisture vaporisation at high temperatures, volume expansion leading to tin splattering.

Moisture in components: If some components are not sealed, they may absorb moisture and cause tin splattering when soldering.

Flux problems

Improper dosage: too much or too little flux may affect the quality of soldering, too much may lead to solvent evaporation, residue decomposition gas.

Abnormal composition ratio: flux containing volatile substances or active agent ratio is not appropriate, may be at high temperatures and violent reaction.

Moisture: If the flux is not sealed and stored, it may absorb moisture, and it is easy to trigger tin splattering when it is used after moisture.

Solder paste quality problems

Expired or deteriorated: solder paste that exceeds the shelf life or improper storage conditions, chemical changes may occur, resulting in the generation of gas when soldering.

Insufficient re-temperature: If the solder paste is not re-tempered sufficiently after it is taken out of the refrigerated environment, the water vapour in the environment will condense on the solder paste, and the moisture will evaporate and heat up quickly, resulting in spattering.

Improper setting of process parameters

Insufficient preheating temperature or time: If the preheating stage is not hot enough or the time is too short, the solvent in the solder is not fully evaporated.

Reflow temperature curve is unreasonable: too large a slope of the temperature rise, the peak temperature is too high or insufficient holding time, may make the solvent or flux in the solder paste react violently.

Operation or environmental problems

Operator hand sweat pollution: soldering, if the operator's hands have sweat or moisture is not wiped dry, may contaminate the solder or PCB.

Environmental humidity is too high: excessive humidity in the production workshop, may accelerate the material moisture absorption, increasing the risk of tin splattering.

II. the solution

Strengthen material control

Strict storage conditions: Solder paste, solder wire, PCB boards and components should be stored in a dry, cool and ventilated environment, PCB boards and components are recommended to be stored in moisture-proof boxes. Solder paste needs to be kept refrigerated, open the cap after it is completely warmed back up, use it up as soon as possible after opening, and the unused portion should be sealed and refrigerated.

Bake before use: For materials that may be affected by moisture (e.g. PCB boards, components), bake at low temperature (e.g. 120°C/2 hours) before soldering to remove moisture.

Check solder paste expiration date: Make sure the solder paste is within its shelf life and check its appearance before use.

Optimise flux usage

Control dosage: Follow the dosage recommended by the solder paste supplier to avoid too much or too little.

Choose the right flux: According to the requirements of the soldering process, choose a flux with a reasonable composition ratio and moderate activity.

Sealed storage: Flux should be sealed immediately after use to avoid moisture or contamination.

Adjustment of process parameters

Optimise the preheating and reflow curves: Adjust the preheating temperature, time and reflow temperature curves according to the type of solder paste and thickness of the PCB board.

Control the slope of temperature rise: avoid too fast temperature rise resulting in violent vaporisation of solvents, generally the slope of temperature rise is controlled at 1-3℃/sec.

Extend the holding time: set the appropriate holding time in the reflow zone, so that the solder fully melted and wet pad.

Improve the operation and environment

Standardise the operation process: require operators to wear anti-static gloves to avoid contamination of materials by sweaty hands; clean the workbench and tools regularly.

Control environmental humidity: install dehumidifiers or air conditioners in the soldering area to control the humidity within 40-60% RH.

Enhance training: Regularly train operators on welding process and quality control.

Equipment Maintenance and Inspection

Regular maintenance of soldering equipment: e.g. reflow oven, wave soldering machine, etc. to ensure accurate temperature control and smooth conveyor belt.

Check solder paste printing quality: Ensure that the solder paste is printed evenly and without leakage or offset.

Select anti-spatter laser solder paste: anti-spatter laser solder paste is specially designed for fast soldering process, which can significantly reduce tin beads and spatter.

Through the above measures, you can effectively reduce the occurrence of soldering paste tin splattering phenomenon, improve soldering quality and product reliability.