Find soldering problems after smt pick and place machine process

In reflow oven patch processing after we finished the smt pick and place machine mounting process, some quality problems often occur, such as: cold joint, bridges, insufficient wetting, too much tin/less tin, what is the reason for this reflow soldering? how to solve it,
The following Qhsmt technology will be explained to you.

One . Parts drift – reasons: 1. The two ends of the parts are heated unevenly. 2. One end of the part does not eat tin well.
Solution: 1. The reflow adopts a saddle type and prolongs the preheating (150~170℃) time. 2. Make sure the parts and PCB pads are free from oxidation.

3. Confirm that the solder coating of the part is compatible with the composition of the solder paste.

Two: Short circuit between BGA solder balls and solder balls—-reasons 1. Too much solder paste 2. Solder paste printing offset 3. Solder paste collapse 4. Squeegee pressure is too small 5. The gap between the steel plate and the circuit board is too large
Solution: 1. Reduce the amount of solder paste printing (reduce the thickness of the steel plate, reduce the opening of the steel plate). 2. Adjust the alignment accuracy of the steel plate. 3. Confirm that the precision of the circuit board assembly meets the requirements. 4. Adjust the Reflow curve. 5. Confirm the quality of solder paste. 6. Increase the pressure and speed of the scraper. 7. Check that the tension of the steel plate meets the regulations and there is no deformation. 8. Check that the thickness of the solder mask and silk screen layer conforms to the regulations

Three: empty welding or pillow effect
Reasons: 1. The amount of solder paste is too small 2. The solder balls do not touch tin 3. Vias-in-pad 4. The circuit board solder pads do not eat tin 5. BGA or PCB high temperature deformation Inconsistent or uneven size
Solution:

1. Increase the thickness of the steel plate or increase the opening. 2. Check whether the solder balls are oxidized. 3. Change the design to fill holes or increase the amount of tin. 4. Check whether the pad is oxidized on the circuit board. 5. Slow down the heating rate, increase the amount of tin, and use a furnace carrier. 6. Review the opening of the steel plate and the printing parameters of the solder paste

Four: Air Soldering – Reasons 1. The feet of the parts are not flat 2. The amount of solder paste is too small 3… The feet of the parts do not eat tin
Solution: 1. Confirm that the flatness of the foot of the part meets the regulations. 2. Increase the thickness of the steel plate or increase the opening. 3. Decrease the heating rate of Reflow or review the tin-eating property of the parts with the supplier. 4. Check whether the foot of the part is oxidized. 5. Change the design to avoid holes when filling holes or solder paste printing. 6. Check whether the circuit board pads are oxidized

Five: Air welding of footless SMD parts
Reasons: 1. Improper design of solder pads 2. Uneven heating at both ends of solder pads 3. Too little solder paste 4. Poor tin consumption of parts
Solution: 1. Check whether the feet of the parts connected to the large-area copper foil on the circuit board dissipate too fast, so that the heating rate cannot keep up with other solder feet. 2. Slow down the heating rate of the temperature curve or the pad size of the same part should be consistent. 3. Increase the amount of solder paste 4. The parts must meet the needs of eating tin

Six: Tombstone/Tombstone – Reasons 1. Inconsistent heating speed at both ends of the pad, improper design of the pad 2. Different tin eating at both ends of the pad 3. Uneven heating at both ends of the pad 4. The reflow temperature is heated too fast
Solution:

1. Increase thermal resistance. 2. Slow down the heating rate of the temperature profile 3. Preheat to 170°C before reflow soldering

Seven: Cold Welding – The Reason

1. The reflow soldering temperature is too low 2. The reflow soldering time is too short 3. The tin-eating problem of the pins
   Solution 1. Increase the peak reflow temperature to 245℃～255℃. 2. Extend the reflow soldering time (>220℃ above at least 40-60 seconds)

you can choose a reflow oven to meets your need like qfr630,qrf835,qrf1235

Also we have different kinds of smt pick and place machine like tvm802a,tvm802b,tvm802ax,tvm802bx,tvm925s,tvm926s,ql41,qm61,qm62,qm81,qm10