PCBA Tech - Type of patch adhesive and SMT solder paste

Type of patch adhesive: In the smt patch processing process, thermosetting patch adhesives are generally used to paste components on the PCB circuit board. The main materials used are epoxy resin, polypropylene, nitrile propionate and Polyester and so on. Commonly used patch adhesives are epoxy patch adhesives and acrylic patch adhesives.

1. Epoxy resin patch adhesive and epoxy resin patch adhesive are the most commonly used patch adhesives in smt patch processing. The main components are epoxy resin, curing agent, filler and other additives, epoxy resin patch The curing method of the sheet glue is mainly thermal curing. Epoxy resin is a thermosetting, high-viscosity adhesive, which can be made into liquid, paste, film, and powder forms. The thermosetting adhesive will not soften after curing and cannot re-establish the bonding connection. Thermosetting can be divided into one-component and two-component.

2. Acrylic patch adhesive. Acrylic patch adhesive is another major type of patch adhesive commonly used in smt patch processing. Its components mainly include acrylic resin, light curing agent and filler, and are light-cured patch adhesives. Acrylic resins are also thermosetting adhesives, which are commonly used as one-component systems. It is characterized by stable performance, short curing time and sufficient curing, easy control of process conditions, storage conditions at room temperature and dark storage, for up to one year, single bond strength and electrical properties are not as high as epoxy type.

Curing. The curing method of the adhesive includes thermal curing and light curing. Light and heat dual curing and ultrasonic curing, etc., of which light curing is rarely used alone. Ultrasonic scratching is usually used for adhesives that use sealed curing agents. The most commonly used curing methods in the Smt patch processing process mainly include thermal curing and UV/thermal curing.

1. Heat curing. Thermal curing is commonly used in two forms: oven intermittent thermal curing and infrared oven continuous thermal curing.

2. UV/thermal curing. The UV/thermal curing system uses both UV irradiation and heating methods, which can cure the adhesive very quickly on a continuous production line.

Selection of patch adhesive: How to select the appropriate patch adhesive to ensure the smooth progress of smt production is the most concerned issue of electronic product technologists. The usual practice is to list the performance indicators of the patch adhesive, see the table, and follow the table In each item, the selected patch adhesives are tested and compared, and good varieties are selected.

How to print SMT solder paste

The tin in the solder forms an alloy with the base metal due to metallurgical reactions during the soldering process, while lead hardly participates in the reaction below 300°C. However, after adding lead to tin, excellent characteristics that neither tin nor lead have can be obtained, which are manifested in the following aspects.

(1) Lower the melting point and facilitate welding. The melting point of tin is 231.9 degree Celsius, and the melting point of lead is 327.4 degree Celsius. Both of them are higher than the melting temperature of solder by 183 degree Celsius. If two metal alloys of tin and lead are mixed, the melting point of the alloy is lower than that of the two metals, so soldering The process is easy to operate.

(2) Improve mechanical properties. Due to the addition of lead, the mechanical properties of the tin-lead metal, both the tensile strength and the shear strength, are more than double that of its single component.

(3) Reduce surface tension. The surface tension of tin-lead alloy is lower than that of pure tin, so it is conducive to the wetting of the solder on the surface of the soldered metal.

(4) Antioxidant. Adding lead to tin can increase the oxidation resistance of solder and reduce the amount of oxidation.