PCBMASTER will guide you to understand how to achieve a soldering yield rate of 99.99% in PCBA assembly.

Author: Jack Wang

Full-Process Optimization Solution

1. The Microscopic Battle of Solder Paste Printing

① Stencil Opening Strategy:

→ For 0.3mm pitch BGA, use trapezoidal openings (upper width 0.28mm / lower width 0.32mm), which can increase the solder paste volume by 18%.

→ The opening rate of the ground pad of QFN devices should be ≥70% to prevent the void rate from exceeding the standard.

② Printing Parameters:

→ When the squeegee pressure is 0.5kg/cm and the speed is 20mm/s, the stencil release effect is optimal.

→ The nano - coated stencil can increase the stencil release rate from 92% to 98%.

2.The Temperature Game of Reflow Soldering

①Curve Optimization:

→ For lead - free soldering, the recommended RTS curve is as follows: the heating rate is 1.5℃/s, the peak temperature is 245℃±2℃, and the liquid time is 45 - 60 seconds.

→ For heat - sensitive components such as LEDs, use local nitrogen protection (oxygen content <500ppm).

②Furnace Temperature Monitoring:

Collect at least 3 groups of data per shift using a KIC temperature measuring instrument, and the CPK value should be ≥1.33.

3. Detection Technology Upgrades

3D SPI (Solder Paste Inspection):

→ The height measurement tolerance is ±5μm, and the volume detection accuracy is ±3%.

X - Ray Layered Scanning:

→ Conduct a 45°tilted scan for PoP packages, which can detect 99% of hidden solder joint soldering defects.

→ The resolution should reach 1μm, and it can automatically classify defects with the help of an AI algorithm.

4. Hard Rules for Material Management

MSL (Moisture Sensitivity Level) Control:

→ MSL3 materials should be used up within 168 hours after opening, and the humidity in the workshop should be <30%RH.

→ Baking conditions: 125℃/24 hours (for humidified chips).

Solder Compatibility:

→ SAC305 solder has the best compatibility with OSP surface treatment, but it is prone to black pads when combined with ENIG.

If you want to know more, please feel free to contact us at  www.pcbmaster.com.

 Author: Jack Wang