PCB News - PCB manufacturer, how to identify the quality of solder paste

PCB manufacturer, how to identify the quality of solder paste

When buying solder paste, it is necessary to provide a certificate of approval, which basically includes the following points:

1. Solder paste performance. 2. Ingredients and their proportions. 3. SGS report. 4. Viscosity qR>p5W. 5. Used for deadlines. 6. Storage time at storage temperature. 7. Defrosting time. 8. Storage temperature. 9. Used for temperature. 10. The temperature storage time of the production workshop.

The use of a solder paste brand and open model must go through a series of preliminary debugging and actual production debugging

The following are common early-stage debugging methods and debugging functions: the debugging projects are divided into two parts:

(1) Debugging of solder paste characteristics:
1. Viscosity debugging The debugging results have a greater impact on solder paste printing and placement;
2. Collapse debugging: C
3. Solder ball debugging: The solder ball debugging is to debug whether small solder balls appear on the PCB surface and component pins after the solder paste is reflowed;
4. Adhesion debugging: Adhesive debugging is very important, for debugging the bonding ability of solder paste to electronic components in the high-speed placement process;

(2) Flux characteristics debugging:
1. Expansion rate debugging: an index to measure the activation performance of solder paste;
2. Debugging of copper mirror (corrosion caused by flux) to debug the corrosivity of flux;
3. Debugging of silver chromate test paper: The debugging method is to use silver chromate test paper to debug whether the flux contains Cl- and Br- solder paste. Save and use it for precautions

Storage method: Since the solder paste is a chemical product, it can be stored in a refrigerator (5~10 degree Celsius) to reduce the activity, increase the life span, avoid placing it in a high temperature place, and easily deteriorate the solder paste

Re-temperature: The activity is greatly reduced during refrigeration, so the solder paste must be placed at room temperature before use to restore the activity to perform the best soldering state.

Stirring: 1. Stirring is to mix the tin powder and Flux evenly, but if the stirring time is too long, the shape and viscosity of the tin powder will be damaged.

2. If there are hard lumps on the surface of the solder paste before mixing, remove the hard lumps on the surface before use.
3. Do not mix solder pastes of different types and brands to avoid undesirable phenomena.

Common solder paste defects
1. Dislocation of the solder paste pattern: the cause of the improper steel plate alignment and the offset of the pad; the printing accuracy of the printer is not enough. Hazard: easy to cause bridging.

Countermeasures: adjust the position of the steel plate; adjust the printing press.
2. The solder paste pattern is sharp and dented. Causes: excessive pressure on the squeegee; insufficient hardness of the squeegee; extra-large window. Hazard: Insufficient amount of solder, false soldering is easy to occur, and solder joint strength is not enough. Countermeasures: adjust the printing pressure; change the metal squeegee; improve the template window design.
3. Too much solder paste: Causes: too large stencil printing size; too large gap between steel plate and PCB; too large gap between steel plate and PCB. Harm: easy to cause bridging. Countermeasures: check the size of the template window; adjust the printing parameters, especially the gap of the PCB template.
Countermeasure: Wipe the template.
4. The graphics are uneven and have breakpoints. Causes: The smoothness of the template window wall is not good; the printing board has too many times and the residual solder paste cannot be wiped off in time; the thixotropy of the solder paste is not good. Hazard: It is easy to cause insufficient solder, such as false soldering defects. Countermeasure: Wipe the template.
5. Graphic contamination: Causes: The stencil was printed too many times and could not be cleaned up in time; the quality of solder paste was poor; the steel plate was jittered when it left. Harm: Easy to bridge. Countermeasures: scrub the steel plate; change the solder paste; adjust the machine.

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