PCB online SMT adhesive glue and dispenser main process parameters

In the PCB on-line chip processing and dispensing process, the main process parameters that can be changed by the SMT adhesive glue and the dispenser are as follows:

(1) Rheological properties of the adhesive glue. The rheological property (thixotropy) of the  adhesive glue in PCB online SMT processing means that the viscosity is quickly lowered at high shear rate, and the viscosity can rise rapidly when the shearing action is stopped. Good rheology ensures that the adhesive glue flows smoothly from the needle and forms a good glue dot on the PCB.

(2) The initial adhesive strength of the adhesive glue. The initial adhesive strength of PCB online SMT processing adhesive glue is the strength of the pre-cured patch adhesive. It should be sufficient to resist the displacement strength of the bonded components.

(3) Glue point outline. The correct glue point profile has two main types: peak shape (also called triangle) and round head shape. The peak shape is formed by a glue with a higher yield value, and the round shape is formed by a glue of a lower yield value. Compared with the peak shape, the formation of a round-shaped dot in the high-speed SMT dispensing process has more desirable bonding characteristics.

(4) The diameter of the glue dot. The dot diameter GD is determined by the NID in the needle and the distance ND between the needle and the PCB.

Since the surface tension between the glue adhesive and the PCB must be greater than the surface tension between the adhesive glue and the needle, the tension is determined by the diameter GD of the glue point and the NID of the needle. For this reason, it is generally required that the two have the following relationship: GD>2NID.

(5) The height of the glue point. The glue dot height R should be at least greater than the pad height A and the SMC/SMD terminal metallization layer height B. The height of the glue dot affects the bonding strength. The ideal bonding strength generally requires that the glued point after the extrusion can adhere or touch at least 80% of the surface of the bonded SMC/SMD bonding zone. For this reason, R>2A+B. is generally taken.

(6) Waiting/delay time. The waiting/delay time from the PCB online dispensing system to the dispensing of the adhesive glue from the needle varies depending on the type of adhesive glue, the structure and form of the syringe and needle, and its structural parameters. Which should be selected and adjusted according to the actual situation , generally between tens and hundreds of milliseconds.

(7) Z-axis recovery height. A reasonable Z-axis recovery height should ensure that the dispensing head has the correct detachment point "bounce off" effect after dispensing, and should not be too high, so as to avoid the waste of the "empty stroke" and reduce the working frequency of the dispensing. If the Z-axis return height is not enough, the glue point will be dragged when the needle moves, causing the drawing phenomenon.

Time/pressure. The time/pressure value of the dispensing is set and adjusted according to the actual conditions of the dispensing device, the adhesive glue and the bonded object. It should be noted that even with the same dispensing system and the same bonding object, the same time/pressure parameters will produce different dispensing effects when the amount of patch glue stored in the dispensing syringe is different.

In short, different SMC/SMD have different process parameters.pcb manufacturer should choose the proper thickness of glue, the number of glue points, the glue point diameter, the dispenser diameter , Process parameters such as pressure and time, coating operating temperature, etc.

according to the type (shape, quality, etc.) of SMC/SMD, the above is the pcb manufacturing industry consultation provided by FASTPCBA, I hope to help you!