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SMT common defects sharing
A tin bead
Before printing, the solder paste was not fully warmed, thawed, and stirred evenly.
2. After printing for too long without reflux, the solvent evaporates and the paste turns into dry powder before falling onto the ink.
3. Printing is too thick, causing excess solder paste to overflow after the component is pressed down.
When REFLOW, the temperature rises too quickly (SLOPE>3), causing boiling.
5. The pressure on the surface mount is too high, and the downward pressure causes the solder paste to collapse onto the ink.
6. Environmental impact: Excessive humidity, normal temperature of 25+/-5, humidity of 40-60%, can reach up to 95% during rain, requiring dehumidification.
7. The shape of the solder pad opening is not good, and no anti solder bead treatment has been done.
8. The solder paste has poor activity, dries too quickly, or contains too many small particles of tin powder.
9. Solder paste exposed to an oxidizing environment for too long absorbs moisture from the air.
10. Insufficient preheating, slow and uneven heating.
11. Printing offset, causing some solder paste to stick to the PCB.
12. The scraper speed is too fast, causing poor edge collapse and resulting in the formation of solder balls after reflow.
13: The diameter of solder balls should be less than 0.13mm, or 600 square millimeters should be less than 5.
B short circuit
1. The steel mesh is too thick, severely deformed, or there is a deviation in the opening of the steel mesh, which does not match the position of the PCB solder pad.
2. The steel mesh was not cleaned in a timely manner.
3. Improper setting of scraper pressure or deformation of scraper.
4. Excessive printing pressure causes blurry printed graphics.
5. The reflux time of 183 degrees is too long (standard is 40-90s), or the peak temperature is too high.
6. Poor incoming materials, such as poor coplanarity of IC pins.
7. The solder paste is too thin, including low metal or solid content in the solder paste, low solubility in shaking, and easy to explode.
8. The solder paste particles are too large, and the surface tension of the flux is too low.
C displacement
1. The steel mesh is too thick, severely deformed, or there is a deviation in the opening of the steel mesh, which does not match the position of the PCB solder pad.
2. The steel mesh was not cleaned in a timely manner.
3. Improper setting of scraper pressure or deformation of scraper.
4. Excessive printing pressure causes blurry printed graphics.
5. The reflux time of 183 degrees is too long (standard is 40-90s), or the peak temperature is too high.
6. Poor incoming materials, such as poor coplanarity of IC pins.
7. The solder paste is too thin, including low metal or solid content in the solder paste, low solubility in shaking, and easy to explode.
8. The solder paste particles are too large, and the surface tension of the flux is too low.
D Monument
1. Uneven printing or excessive offset, with thick tin on one side and high tensile force, and thin tin on the other side and low tensile force, resulting in one end of the component being pulled towards one side to form a solder gap, and the other end being pulled up to form a monument.
2. Surface mount offset causes uneven force distribution on both sides.
3. One end of the electrode oxidizes, or the electrode size difference is too large, resulting in poor tinning performance and uneven force distribution at both ends.
4. The width of the solder pads at both ends is different, resulting in different affinities.
5. After solder paste printing is left for too long, FLUX evaporates too much and its activity decreases.
6. Insufficient or uneven preheating of REFLOW, with high temperatures in areas with fewer components and low temperatures in areas with more components. The areas with higher temperatures melt first, and the tensile force formed by soldering is greater than the adhesive force of solder paste to the components, resulting in uneven stress and causing the monument to be erected.
E air welding
The temperature of the board surface is uneven, with higher temperatures at the top and lower temperatures at the bottom. The solder paste melts below first to disperse the tin, and the temperature below can be appropriately reduced.
2. There are test holes around the PAD, and solder paste flows into the test holes during reflow.
3. Uneven heating causes the component pins to become too hot, resulting in solder paste being drawn onto the pins and insufficient solder on the PAD.
4. Insufficient amount of solder paste.
5. Poor coplanarity of components.
6. The pins are soldered or there are wiring holes nearby.
7. Insufficient tin moisture.
8. Too thin solder paste causes tin loss.
