Red glue common problem and solution

1. Analysis of common failures of scraping glue:

Before printing, the red glue is usually stirred to reduce its viscosity and facilitate construction. During the construction process, the steel mesh should be cleaned frequently.

a. Glue overflow: caused by too low glue viscosity or too wide steel mesh seam width.

b. The glue does not fall off the scraper during machine scraping: it may be due to the scraper surface being too rough or the red glue specific gravity being too low; or the ambient temperature being too low; the red glue thixotropic index being too high, etc.

c. Too little glue: usually the steel mesh seam width is too small or the steel mesh is not clean, and the holes have been blocked.

d. Red glue collapse: due to poor thixotropy of the red glue; or too fast moisture absorption.

2. Analysis of common faults in dispensing:

After the red glue used for dispensing is dispensed into the dispensing tube, it must be degassed again. A small bubble can cause many pads to have no glue.

(1) The dispensing needle should be cleaned in time.

(2) Analysis of common defects in dispensing:

Common defects include: drawing, no glue dots, discontinuous glue dots and satellite glue dots.

a. Drawing will cause pad contamination. Drawing may be caused by the following reasons: too high glue viscosity; too low dispensing temperature; too little glue output; too large distance between the needle and the PCB board or other seemingly unrelated reasons, such as electrostatic discharge to the PCB board; the PCB board is too soft or too hard.

b. No glue dots may be caused by too low dispensing pressure; the needle nozzle is blocked or there are bubbles in the red glue, etc.

C. Discontinuous glue dots may be caused by the needle nozzle leaving the ground support and falling on the pad; insufficient recovery time allocated to the glue; insufficient pressure, etc.

c. When satellite points appear, it may be helpful to reduce the height of the needle nozzle from the ground, or if the amount of glue discharged is too large relative to the needle nozzle, the dispensing pressure can be reduced; using a needle nozzle with a larger inner diameter is also an option.

3. How to deal with dropped parts:

1. When to drop parts: 1) before curing; 2) after curing; 3) after wave soldering.

2. Original red glue: determine which red glue is used to ensure that the sample and goods are not mistaken.

3. Dropped components: capacitors, resistors, glass diodes, ICs and other specific components and component sizes.

4. Drop rate: A drop rate of less than 3/1000 is considered normal drop. Drop rate of various components.

5. 

6. Whether green oil is dropped:

1) If the circuit board drops green oil, it means that there is a problem with the circuit board;

2) The red glue surface at the location where the component is dropped is smooth and flat. It means that the component has a release agent and other reasons.

3) The circuit board and components at the location where the component is dropped are stained with red glue, indicating that the quality of the red glue is problematic. It is recommended to replace the red glue.

7. Red glue curing curve: Strictly grasp the red glue curing curve. If the heating rate is too high, the components are prone to displacement and drop after curing.

7. Component thrust:

Normal measurement of the thrust of 0603 components. Generally, customers are asked to recommend 20 0603 components.

1. If the glue scraping force is below 4KG, it means that the glue is not completely cured.
2. Glue dispensing: The glue dispensing force of 0603 components with an inner diameter of 0.55mm is above 2.5KG. If it does not reach 2.5KG, it means that the glue is not completely cured.

Specific reasons for dropped parts: ※ Focus on 0603 resistors

Component classification:

1. Conventional components: chip resistors, capacitors.

2. Special-shaped components: IC, glass diode, transistor (plastic surface)

1. Dropped components: (1) Conventional R, C

1) Glue quality problem, whether the glue model is matched.

2) Oven temperature: strictly set the furnace temperature according to the furnace temperature curve of the specific product model;

3) Measure the thrust, 0603 is greater than 4KG thrust.

2. Special-shaped components:

(1) IC:

1) The glue surface is smooth and the IC itself has problems.

2) The glue is disconnected from the middle, and the glue quality problem.

(2) Diode:

Smooth and ink on the glue, the component or circuit board itself has problems.

Solution:

1. For diodes and ICs, choose glue with low viscosity;

2. Increase the amount of glue. (Change to a larger-diameter dispensing head and increase the opening of the steel mesh)

3. Ensure that there is no release agent or other chemicals that affect the adhesive and curing on the component.