What can I do to fix dry solder paste?

Solve solder paste drying problem

1.preventive measures in detail

In order to effectively prevent solder paste drying, we need to start from the three aspects of temperature control, dispensing management and mixing details:

Temperature control

Strictly avoid directly open the lid back to the temperature, the solder paste should be placed in a sealed state, the use of constant temperature box back to room temperature, to prevent condensation pollution.

If the ambient humidity is greater than 60%, use desiccant to wrap the solder paste can after rewarming to further absorb moisture and keep the solder paste dry.

Dispensing management

Use small volume packaging (e.g. 30cc syringe) to reduce exposure time after opening and reduce the risk of oxidation.

Refrigerate the remaining solder paste immediately after dispensing to avoid multiple re-warming cycles, - Maintaining solder paste quality.

Mixing Details

Use a plastic scraper for manual mixing to avoid oxidisation and deformation of the solder powder caused by metal scraper.

Stir the paste in a figure-of-eight pattern until the paste is fine and glossy, with no particles.

Conduct viscosity test after mixing to ensure that the qualified range (usually 150-250 Pa-s, adjusted according to the specific model).

2.the precise processing of the dried solder paste

For the dried solder paste, the following measures need to be taken to deal with:

Mixing old and new solder paste

Only the same brand and the same type of paste mixing, to avoid the reaction of different activity levels of flux.

Re-test the paste expansion rate after mixing to ensure that it is greater than 80%.

3. Screening criteria for high quality solder paste

In order to ensure that the purchase of high-quality solder paste, you need to pay attention to the following key parameters and certification requirements, see the table below:

Key indicators

High Quality Solder Paste Characteristics

Risk of poor quality solder paste

Flux Halogen Content

Halogen free or low halogen (<500ppm)

High halogen (high corrosion risk)

Viscosity stability

Viscosity change <10% in 24 hours

Variability >20% (prone to delamination and drying)

Certification Requirements

Adoption of IPC-J-STD-005

ISO 9001 certified

No or incomplete certification (no guarantee of quality)

When selecting solder paste, priority should be given to products that meet the above criteria to ensure the quality and reliability of the paste.

4. Risky operation warning

When dealing with dried solder paste, the following risky operations should be noted:

Scrap criteria for dried solder paste

When there are hard lumps, obvious delamination or sour smell, it needs to be forced to scrap and cannot be repaired.

When ≥10% of less tin or collapsed defects appear after printing, it should be stopped immediately.

Process environment monitoring

During the printing and use of solder paste, the temperature and humidity of the environment meet the requirements of the technical specifications of the solder paste, and the DC wind should not blow on the solder paste.Humidity paste to absorb moisture in the air, easy to cause fried tin, oxidation corrosion and other defects, humidity is too low, the solvent evaporation rate is fast, the paste is easy to oxidise, drop pieces, adhesion decline and other defects

5.Case Study

Case: automotive electronics factory solder paste dry leads to false soldering

Phenomenon: Poor wetting of PCB solder joints, ICT test failure rate increased.

Root cause analysis:

Workshop humidity down to 20%, accelerating solvent evaporation, resulting in dry solder paste.

Operators are not in accordance with the norms of packaging, open the lid several times a day to take, increasing the contact time between the solder paste and air.

Solution:

Add workshop humidifier, the humidity will be stabilised to 45% ± 5%, slowing down the solvent evaporation.

Switch to syringe loading to reduce the exposure time of solder paste.

Through the implementation of the above measures, the automotive electronics factory successfully solved the solder paste dry caused by the problem of soldering, improve the welding quality and product reliability.This fully demonstrates the importance of preventive measures, precise handling, high quality screening, risk warning and case studies in solving the dry solder paste problem.