PCB manufacturing smt defect cause analysis
In the PCB manufacturing process, for PCB manufacturers due to the influence of the error, it is easy to cause PCBA SMT defects, such as: air welding, short circuit, erect, short, tin beads, squatting, floating high, wrong parts, cold welding, the white/reversal, offset printing, the element damage, tin accumulation, gold finger glue, etc., need to analyze these defects, improving product quality.
Analysis of defects in PCB manufacturing SMT processing
First, air welding
1. Weak solder paste activity;
2.Poor opening of steel mesh;
3, Copper or platinum spacing too large or large copper mount small components;
4.Excessive blade pressure;
5.Uneven (warped and deformed) pinof components;
6.The reheating zone of the reflowfurnace heats up too fast;
7.PCB copper platinum too dirty or oxidation;
8.PCB board contain water;
9.Deviation of machine placement;
10.Solder paste printing offset;
11. The loose guide rail of the machine fixture causes the mounting deviation;
12.MARK points are misaligned due to misalignment of components, resulting in blank weldingduring pcb manufacturing;
Second, short circuit
1.The distance between the stenciland the PCB is too far, resulting in too thick and short solder paste printingduring pcb manufacturing;
2.The mounting height of components is set too low to squeeze the solder paste and cause a short circuit;
3.The heating furnace heats too fast;
4.Caused by component offset mounting;
5.Poor opening of steel stencil(too thickcause too long opening and too large opening);
6.The solder paste cannot bear the weight of components;
7.The deformation of steel stencilor scraper causes the solder paste printing to be too thick;
8.Strong activity of solder paste;
9.The sealing tape at the empty paste point is rolled up to make the solder paste printing of peripheral components too thickduring pcb manufacturing;
10. Reflow vibration is too large or not horizontal;
1.The copper and platinum on both sides of different sizes produce uneven tension;
2.The speedof preheating is too fast;
3.Deviation of machine placement;
4.Uneven solder paste printing thickness;
5.Uneven temperature distribution in the reflowfurnace;
6. Solder paste printing offset;
7. The machine track fixture is not tight, resulting in placement deviation during pcb manufacturing;
8.Shake the machine head;
9.The solder paste is too active;
10.The furnace temperature is not set correctly;
11.The spacing between copper and platinum is too large;
12.MARK point misoperation
Fourth, missing parts
1.Insufficient vacuum of carbon plate of vacuum pump, resulting in missing partsduring pcb manufacturing;
2.The nozzle is blocked or defective;
3.Improper component thickness detection or defective detector;
4.Improper placement height;
5. Suction nozzle is too large or not blowing;
6.Improper nozzle vacuum setting (applicable to MPA);
7.The speed of placing special-shaped components is too fast;
8.Trachea head is very fierce;
9.Valve seals wear;
There are elements on the wipe plate of foreign body on the track side of reflow furnace;
Fifth, tin beads
1.Insufficient preheating of reflow welding and excessive heatingduring pcb manufacturing;
2.Refrigerate the solder paste with incomplete temperature;
3.Solder paste absorbs spatter (excessive indoor humidity);
4.Too much water on PCB board;
5.Add excessive diluent;
6.Improper opening design of steel stencil;
7.Tin powder particles are uneven.
Sixth, offset amount
1.The positioning reference point on the board is not clear
2.The positioning reference point on the circuit board is not aligned with the reference point of the template.
3.The fixing clamp of the circuit board in the printing machine is loose, and the locating thimble is not in place.
4.The optical positioning system of the printing machine is faulty
5.The lack of solder paste template openings and circuit board design document is inconsistent during pcb manufacturing
In order to improve the defects of the PCBA , it is necessary to carry out a rigorous inspection of all aspects to prevent problems of the previous process from flowing as little as possible into the next process.
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