Explanation of defects in SMT reflow soldering products

The welding defects in SMT reflow soldering products can be divided into main defects, secondary defects, and surface defects. Any defects that result in functional failure of the circuit board after reflow soldering are referred to as major defects; Minor defects refer to defects where the wetting between solder joints is still good, which will not cause the loss of circuit board function after reflow soldering, but may affect the product's lifespan; Surface defects refer to those that do not affect the functionality and lifespan of the product.

Based on years of experience, JEENOCE divides electronic products into three categories: consumer devices such as TVs and VCDs; Specialized equipment, such as measuring instruments and communication; High reliability equipment, such as spacecraft and pacemakers.

Different production departments can decide whether to repair minor and surface defects based on the IPC-A-610B standard and the nature of their own products. For surface defects, they should also be repaired before a specific appearance is required or accurately identified.

1、 The main defects of common SMT reflow soldering

1. Bridging

The connection between unwanted metal components caused by solder can cause short circuits. This defect occurs in various component solder joints and must be repaired when it occurs.

2. Erect a monument

Monuments, also known as drawbridges, Manhattan, and tombstones, are common defects in SMT production, mainly appearing on lightweight chip resistive and capacitive components.

3. Misalignment

An open circuit state occurs when the position of the component moves, and various component pins will occur.

4. Solder paste not melted

After SMA is soldered in a reflow furnace, there is a phenomenon of solder paste not melting on the pins of various components.

5. Material suction/core suction phenomenon

Solder is not wetted at the root of the component pins, but rises to the junction between the pins and the component body through the pins, like oil in an oil lamp rising to the upper end of the wick, commonly found in QFP and SOIC.

2、 Common secondary defects after SMT reflow soldering

The wetting effect of the solder pads is acceptable and will not cause the loss of SMA function, but it will affect its lifespan. In production inspection, standards 1, 2, and 3 are formulated based on welding quality, and different welding qualities determine the quality of the product.

For chip components, excellent solder joints should have a smooth, shiny, and continuous appearance, gradually thinning the straight edges, and the bottom layer at the tip should not be exposed, nor should sharp protrusions appear. The position of the components does not deviate, and there are cracks, notches, and damages in the components, as well as the phenomenon of electrodialysis at the ports.