PCBA board analysis of quality defects and causes

1. Cold welding refers to solder joints with insufficient wetting. Features: gray, dull appearance. When observed under a microscope, the solder joints were in the form of particles. The main reason is that the temperature curve of the reflow furnace is improperly set, the speed of the furnace is too fast, the product is placed too densely, and the solder paste is deteriorated.

2. Connecting tin means that two or more solder joints are connected together, resulting in a short circuit. Features: Two pins are connected together. The main reason: tin paste printing with tin, solder paste collapse, etc.;

3. Virtual soldering means that the component pins are not properly connected to the PCB welding pads. Such anomalies are most likely to occur in SMT welding anomalies. Features: Pins are not connected to welding pads, or pins are wrapped by solder but not connected. Main reasons: component lead or pad oxidation, deformation, contamination, design size mismatch, printing, mount offset, furnace temperature settings do not match, etc.;

4.Monument, also known as the tombstone. Features: One end of the component soldering is not connected to the line and is upturned.

The main reason: improper design of the product causes uneven heating at both ends of the component, offset of the mounting surface, oxidation or contamination of the welding pad or component pin, one end of solder paste is not printed or offset;

5.Sideways. Features: Although the two ends of the component are soldered together, the wide side of the component is perpendicular to the PCB. The main reason: because the component packaging is too loose, the equipment is improperly debugged, resulting in mounted flying parts, smearing in the process of passing the furnace;

6. Turn over. Features: The silky surface of the component that was originally facing up is attached to the bottom. Such anomalies do not affect the implementation of product functions, but have an impact on maintenance. The main reason: the packaging of the components is too loose, the equipment is improperly debugged, resulting in the mounted flying parts, and the products are subjected to strong vibration during the furnace process;

7.Tin beads. Features: Round particle solder balls exist in the non-welded area of the PCB. The main reason: the moisture of solder paste is not enough time, the reflow temperature is not properly set, the stencil is not properly opened, etc.

8. Pinholes. Features: There are pinholes on the surface of the solder joint. Main reasons:moisture of welding materials, improper reflow temperature, etc.