Common Problems of Dispensing Nozzles

1. Stringing/Tailing

Causes

Stringing or tailing is a common defect in dispensing. Typical causes include an excessively small dispensing nozzle inner diameter, excessively high dispensing pressure, excessive distance between the nozzle and the PCB, expired or poor-quality solder paste, overly high solder paste viscosity, insufficient temperature recovery after removal from the refrigerator, and excessive dispensing volume.

Recommendations:Replace with a nozzle with a larger inner diameter; reduce dispensing pressure; adjust the "stop" height; replace the solder paste with a type of appropriate viscosity; allow the solder paste to return to room temperature (approximately 4 hours) after being taken out of the refrigerator before production; adjust the dispensing volume.

2. Nozzle Clogging

Causes

The fault is characterized by insufficient or no adhesive discharge from the nozzle. Common causes include incomplete cleaning of the needle hole, blockage due to impurities mixed in the solder paste, and mixing of incompatible adhesives.

Recommendations:Replace with a clean needle; use high-quality solder paste; ensure the correct solder paste grade is selected.

3. Dry Firing

Causes

The phenomenon involves dispensing actions without actual adhesive discharge. Main causes are air bubbles mixed in the solder paste and nozzle clogging.

Recommendations:Degas the adhesive in the syringe (especially for manually filled adhesive); replace the clogged nozzle.

4. Component Misalignment

Causes

After solder paste curing, components shift—severely, component pins may deviate from the pads. Causes include uneven adhesive discharge (e.g., uneven glue volume at two points for chip components), component displacement during placement, low initial adhesion of the solder paste, and semi-curing of the adhesive due to prolonged storage of the PCB after dispensing.

Recommendations:Inspect the nozzle for clogging to eliminate uneven adhesive discharge; adjust the placement machine's working status; replace the solder paste; avoid prolonged storage of the PCB after dispensing (storage time should be less than 4 hours).

5. Component Falling Off After Wave Soldering

Causes

The adhesive bond strength of cured components is insufficient (below the specified value), and components may fall off when touched. Causes include inadequate curing process parameters (especially insufficient temperature), excessively large components with high heat absorption, aging UV curing lamps, insufficient adhesive volume, and contamination of components or PCBs.

Recommendations:Adjust the curing profile—especially increase the curing temperature (the peak curing temperature for thermal curing adhesives is generally around 150℃; failure to reach the peak temperature easily causes component falling off). For UV-curing adhesives, check for aging curing lamps (e.g., blackened tubes); also consider factors such as adhesive volume and contamination of components/PCBs.

6. Component Pin Floating/Shifting After Curing

Causes

After curing, component pins float or shift. During wave soldering, solder may seep under the pads, leading to short circuits or open circuits in severe cases. Main causes are uneven adhesive application, excessive adhesive volume, or component misalignment during placement.

Recommendations:Adjust dispensing process parameters; control the adhesive volume; optimize the placement process parameters.