PCBA Tech - Cleaning requirements for dust-free shop after SMT patch processing and welding

Cleaning up after SMT processing and bonding in PCBA processing plant refers to removing SMT reflux welding, solder residue on the surface layer of surface layer after peak welding and manual welding by using physical effect and chemical reaction method, as well as pollutants caused by SMT processing and assembling process, and hazards to surface layer assembling board caused by pollutants in the process flow of the process.

1. The activating agent added in the solder and the solder sound contains a small amount of westernized substance, acid, or salt, which results in residual impurities covering the surface layer of SMT solder joints. When the electronic equipment is powered on, the residual impurities ions will migrate toward the conductor with opposite polarity, which will cause short circuit in serious cases.

2. Halogens in common solders at present stage, chlorides have very strong activity and hygroscopicity. In Hunan wet environment, they corrode the base plate and solder joints, reduce the insulation resistance of the surface layer of the base plate and generate electrical migration. When the situation is serious, they conduct electricity and cause short circuit or break.

3. The SMT processing of PCBA plants for high-standard military products, medical products, instruments and other products with special requirements needs to be treated with three-proof treatment. The standard before the three-proof treatment has a high degree of cleanliness, otherwise in relatively adverse environmental conditions such as hot flashes or high temperatures, it will cause serious consequences such as reduced or invalid electrical performance.

4. Due to the fast shielding of residual impurities after welding, the probes for on-line or functional time measurement are not in good contact and are prone to errors.

5. For high-standard products, some defects such as thermal damage and spallation cannot be exposed by SMT due to the shielding of residue after welding, which results in leakage and affects the reliability. At the same time, more impurities also affect the appearance of the baseboard and the commodity of the board.

6. Post-weld debris will affect the connection reliability of high density, multi-I/O junction array chips and inverted chips.

In general, there are several requirements for dust-free environment in SMT processing workshops. First, the load-bearing capacity, vibration and noise requirements of the workshops, the bearing capacity of the workshops'pavement should exceed 8KN/m2, and the vibration should be controlled within 70dB, with the maximum value not exceeding 80dB.

SMT processing workshop requires air source. It is equipped with the pressure of air source according to the requirements of equipment. It can use the air source of the factory. It can also be equipped with oil-free compressed air machine independently. Generally, the pressure is more than 5kg/cm2. Cleaning up and drying of purified air is required. Therefore, compressed air must be deoiled, dedusted, wastewater treated, and used as gas pipeline with stainless steel plate or pressure-resistant plastic hose. There are also exhaust system requirements, reflux welding substitutes factory furnaces and peak welder equipment need to be equipped with exhaust fan.

SMT processing workshop must maintain daily cleanliness, no dust, no corrosive vapor, cleanliness control is required in the production shop, cleanliness control is in: 500,000 grade, the best working temperature of the production shop is 23 +3 C, generally 17-28 C, air humidity is 45%-70%RH, set appropriate temperature and humidity meter according to the specifications and dimensions of the production shop for regular supervision. And equipped with equipment to adjust temperature and humidity.