PCBA Tech - Analysis of the causes of bad PCBA patch

During the production process of PCBA patch, due to the influence of operation error, it is easy to cause the defects of PCBA patch, such as: empty soldering, short circuit, standing upright, missing parts, tin balls, rising feet, floating height, wrong parts, cold welding, reverse Direction, reverse white/back, offset, component damage, less tin, more tin, golden finger sticky tin, glue overflow, etc. These defects need to be analyzed and improved to improve product quality.

1. Air welding

The specificity of the red glue is weak; the mesh plate is not well opened; 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 components is not good (lifting feet, deformation) reflow furnace preheating zone heating up too fast ; PCB copper platinum is too dirty or oxidized;

The PCB board contains moisture; the machine placement is offset; the red glue printing is offset; the machine's plywood track is loose and the placement is offset; the MARK point is misilluminated and the component is biased, resulting in empty soldering;

Two, short circuit

The distance between the stencil and the PCB board is too large to cause the red glue printing to be too thick and short circuit; the component patch height is set too low to squeeze the red glue to cause a short circuit; Poor (too thick, too long pin openings, too large openings); red glue cannot bear the weight of the component; deformation of the screen or squeegee causes the printing of red glue to be too thick; the specificity of red glue is strong; empty dots The roll-up of the seal sticker paper causes the red glue printing of the peripheral components to be too thick; the reflow soldering vibration is too large or not level;

Three, stand up

The difference in size on both sides of copper and platinum causes uneven tension; preheating rate is too fast; machine patch deviation; red glue printing thickness is uniform; temperature distribution in the reflow furnace is uneven; red glue printing deviation; machine track splint is not tight Cause the patch to shift; the machine head shakes; the red glue is too specific; the furnace temperature is set improperly; the copper-platinum spacing is too large; the MARK point is misphotographed and the yuan is biased

Four, missing parts

Vacuum pump carbon sheet is not good enough vacuum leads to missing parts; suction nozzle clogged or poor suction nozzle; improper component thickness test or poor detector; improper setting of patch height; suction nozzle blowing too much or not blowing; suction nozzle vacuum setting improper (Applicable to MPA); The patching speed of special-shaped components is too fast; the head trachea is severely broken; the valve sealing ring is worn; there is a foreign body on the side of the reflow furnace track to wipe off the board components;

Five, tin beads

Insufficient preheating of reflow soldering and too fast heating; Red glue is refrigerated and the temperature is incomplete; Red glue absorbs moisture and causes splashing (indoor humidity is too heavy); Too much moisture in the PCB board; Add excessive thinner; Mesh plate opening design Improper; uneven tin powder particles.

Six, 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 mold thimble is not in place; the optical positioning of the printing machine System failure; the solder paste omission of the printed screen hole does not conform to the design document of the circuit board. To improve the defects of PCBA patch, it is necessary to carry out strict checks in all aspects to prevent the problems of the previous process from flowing to the next process as little as possible.