SMT red glue is certain type of temperature-set adhesive that is used during the SMT process to fix certain components to the board in circumstances where they might lose connection or fall off before solder reflow takes place. Due to the fact that the viscosity, fluidity, wetting and other properties of the adhesive red glue are affected by temperature, it should be used under certain special conditions. We'll discuss these today.
SMT red glue caracteristics:
While lead-free solder paste will melt at around 180º Centigrade (~356º Fahrenheit), SMT adhesive already starts curing at around 105º C, keeping SMT components firmly in place before the solder paste reflows. SMT adhesive has unique properties of viscosity, temperature, and wetting. For example,1`
1. The higher the curing temperature and the longer the curing time, the stronger the bonding strength;
2. Low temperature curing and time: 100 to 120°C, 60-120 seconds; high temperature curing: 150 °C, 90-120 seconds(stronger bond);
1. SMT adhesive should be kept in the refrigerator at 2-8º °C to prevent major impact on the features.
2. It should be raised to and maintained at a room temperature for about 4 hours before usage, and should be used in the order of First-In-First-Out (FIFO).
3. SMT adhesive comes in hardshell tubes with a syringe-like end to push out the material.The glue inside the tube should be pushed to the nozzle to make sure there are no air bubbles in there somewhere (think of ketchup). Red glue that has not been used up, should be put back into the refrigerator for preservation. Old glue cannot be mixed with new ones, so try to use up at least a single tube for that day's application.
The process of Applying Red Glue:
Component placement method and stencil design are determined by the type of parts, the performance of the base material, its thickness, hole size, and shape.
The process of applying red glue differs from that of solder paste. The trepanning of steel mesh can be directed according to the position of the patch pad. In this way, the solder paste can be directly leaked on the PCB pad for further welding. But the red glue steel mesh is special. Its function is to brush the glue and paste the components, making them convenient to weld so that the trepanning is between the device welding plates.
Dispensing method: This method uses compressed air to put the red glue to the substrate through the special dispense head. The glue point’s size and number are controlled by time, pressure pipe diameter and other parameters. The point glue machine has flexible functions. For different components, we can use different dispensing heads and set different parameters. The glue point’s shape and number can also be changed. We can adjust the working parameters, speed, time, air pressure and temperature to achieve a good result.
Finally, the product produced from red glue curing needs to be put through a thrust test as shown below: Only when the appropriate parameters are developed and the rules followed can a high-quality SMT product be obtained.
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