SMD adhesive composition, storage and use process requirements

1. The composition of the SMD adhesive

The SMD adhesive is usually composed of a matrix resin, a curing agent, and a curing accelerator, a toughening agent, a filler etc.

1) Matrix resin.

The matrix resin is the core of the SMD adhesive, and epoxy resin and acrylate polymer are generally used. Polyurethanes, polyesters, silicone polymers, and epoxy-acrylate copolymers have also been used in recent years. Epoxy is the most widely used in high-speed dispensing systems. Epoxy resin has good adhesion to printed circuit boards, very good electrical properties, good dropability, consistent contour and size, high wet strength and cure strength, fast cure, flexibility and Resistance to temperature shocks and other advantages.

2) Curing agent and curing accelerator.

The function of the curing agent and the curing accelerator is to cure the bonding material at a certain temperature for a certain period of time. Epoxy resins are commonly used in amine curing agents (such as diethylamine, diethylenetriamine), acid liver curing agents etc.

3) Toughener

To compensate for this deficiency, a toughening agent is often added to the formulation because the matrix resin is relatively brittle after curing. Commonly used toughening agents are dibutyl phthalate, dioctyl phthalate etc.

4) Filler.

The addition of the filler can improve the electrical insulation performance and high temperature resistance of the SMD adhesive, and can also obtain suitable viscosity and bonding strength of the adhesive. Commonly used fillers are silicon micropowder, calcium carbonate, bentonite machine white carbon black etc.

2. Storage requirements for SMD adhesive

1) Epoxy resin patch adhesive should be stored at 5~10 °C. Acrylic patch adhesive should be stored at room temperature and protected from light.

2) Take the temperature back from the refrigerator one day before use, generally returning temperature for at least 4h.

3) Dispensing process or printing process should be carried out at room temperature (23 ± 3) ° C. 4)

4) The time when the SMD adhesive is exposed to the air and does not work for more than 180 minutes, if it exceeds 180 minutes, it should be recycled and stirred. Each used SMD adhesive should be collected in a clean box and sealed. If it is not used within 48 hours, it should be stored in the refrigerator.

5) After the opening, the SMD adhesive is exposed to the air for more than 5 days and should be scrapped. The SMD adhesive removed from the refrigerator should be stored at room temperature for more than 15 days after being stored. After confirmation, it should be scrapped.

6) The SMD adhesive can be stored for 7 days at room temperature, more than 6 months at less than 5 ° C, and stored for more than 30 days at 5 to 25 ° C.

3, Surface assembly process requirements for SMD adhesive

1) The service life is long at normal temperature.

2) Suitable viscosity.

3) Good thixotropy. It does not deform after coating, does not flow, and can maintain a sufficient height.

4) Fast curing.

5) The bonding strength is appropriate. The shear strength of the SMD glue is usually 6-10MPa.

6) No gas should be generated after curing and welding, and should be compatible with the chemical in the subsequent process without chemical reaction.

7) Does not interfere with circuit function

8) Available in color for easy inspection