PCB Technical - poor pcba labor and materials and insufficient gloss

1. Reasons for bad PCBA labor and materials

In the process of PCBA processing and production, it may be affected by some operational errors, resulting in adverse reactions to the patch. What are the general reasons? The following PCBA contract labor and materials editor will take you to take a look.

1. stand up

The difference in size on both sides of copper and platinum causes uneven tension; preheating rate is too fast; machine placement deviation; solder paste printing thickness uneven; temperature distribution in the reflow furnace is uneven; solder paste printing deviation; machine track splint is not Tightness leads to mounting deviation; machine head shaking; solder paste activity is too strong; furnace temperature setting is improper;

2. Short circuit

The excessive distance between the stencil and the PCB board causes the solder paste printing to be too thick and short-circuit; the component mounting height is set too low to squeeze the solder paste and cause a short circuit; Poor (thickness is too thick, the pin opening is too long, the opening is too large); the solder paste cannot bear the weight of the component; the deformation of the stencil or the squeegee causes the solder paste to be printed too thick;

3. Offset

The positioning reference point on the circuit board is not clear; the positioning reference point on the circuit board is not aligned with the reference point of the screen; the fixed clamping of the circuit board in the printing machine is loose, and the positioning thimble is not in place; the optical positioning system of the printing machine Malfunction; the solder paste is missing the printing screen hole and the design file of the circuit board does not match.

4. Missing parts

The carbon sheet of the vacuum pump is not good enough to cause missing parts; the suction nozzle is blocked or the suction nozzle is bad; the component thickness detection is improper or the detector is bad; the mounting height is set improperly; the suction nozzle blows too much or does not blow; the head trachea is broken; The sealing ring of the gas valve is worn out; there is a foreign body on the side of the reflow furnace track to wipe off the components on the board;

5. Empty welding

The solder paste activity is weak; the stencil opening is not good; the copper-platinum spacing is too large or the copper is attached to small components; the scraper pressure is too large; the flatness of the component feet is not good (the feet are tilted, deformed) Fast; PCB copper platinum is too dirty or oxidized; PCB board contains moisture; machine placement offset

2. Reasons for insufficient luster of solder joints in SMT processing

In SMD processing and soldering technology, many customers usually have requirements for brightness of solder joints. In the process of patch processing and welding, there is no guarantee that the brightness of each welding point can meet the requirements. So what is the reason for insufficient luster of solder joints? The following is the editor of Tongsen Electronic Technology for everyone to introduce.

In SMD processing and soldering technology, many customers usually have requirements for brightness of solder joints. In the process of patch processing and welding, there is no guarantee that the brightness of each welding point can meet the requirements. So what is the reason for insufficient luster of solder joints? The following is the editor of Tongsen Electronic Technology for everyone to introduce.

1. The tin powder in the solder paste is oxidized.

2. Solder paste has additives in the flux itself to form matt.

3. In solder joint processing, the preheating temperature of reflow soldering is low, and the appearance of solder joints is not easy to produce residual evaporation.

4. The solder joints with rosin or resin residue appear after PCB soldering. In actual operation, especially when rosin solder paste is selected, although rosin and non-clean flux will make the solder joints brighter, they often appear in actual operation. However, the presence of residue often affects this effect, especially in larger solder joints or IC pins. If it can be cleaned after soldering, the gloss of solder joints should be improved.

5. Because the brightness of the PCB solder joints is not standard, there will be a certain distance between the solder-free solder paste products and the soldered products after the silver solder paste. This requires customers to choose solder paste suppliers to clarify the requirements for solder.