How to Apply Surface Mount Adhesives on Pcbs Perfectly

Adhesives happen to be an ignored and often taken-for-granted component in surface mount PCB assembly operations. Used mostly for holding components onto the circuit board until the solder joint is formed, adhesives can have both a passive as well as active role to play in the completion of the PCB assembly process. However, when your selection of surface mount adhesives is properly managed and the dispensing system for the same is tweaked considerably, you can expect to achieve dramatic improvements in your process yield. This articles touches upon that point and gives a brief account of how one should apply surface mount adhesives on PCBs perfectly:

Dual Dot Application

Surface mount adhesives are usually dispensed in single dot or double dot applications. Adhesives adhere to surfaces in a way that is directly proportional to the area being joined to the surface. Therefore, components with smaller areas are joined using a single dot of adhesive while larger components need dual dot adhesive applications. These factors need to be borne in mind when designing your PCB assembly process.

Dispensing capabilities

When dispensing surface mount adhesives to the circuit board, one must maintain tight control over the volume of the adhesive being released onto the surface. IPC Class 3 directives necessitate that the adhesive material should not come into contact with solder pads. With all these factors in mind, your adhesive dispensing nozzles and pressure parameters should be tweaked to ensure tight control over the dot diameter and adhesive volume dispensed.

Tackiness and strength

When using surface mount adhesives, you must take its cured and green strength into account so as to calibrate your PCB assembly process appropriately. Your circuit board will have to withstand rapid acceleration and deceleration throughout the components placement cycle and this process might end up displacing the surface mount devices if the adhesive used doesn’t possess adequate tackiness and strength to hold them in place. Make sure you take these factors into account when handling your surface mount adhesive application process.

Dot diameter and volume

An undersized surface mount adhesive dot will not provide enough tack to hold components in place while an oversized one will compromise the circuit board integrity. The height of the components from the circuit board will also have a bearing on the diameter of the adhesive dot required to properly hold them in place. These factors need to be carefully managed for your adhesive application process to yield perfect results.

Pad spacing parameters

PCBs that require the deposition of adhesives will have adequate spacing between solder pads to properly hold this material in place and prevent slump and spillage. On the other hand, PCBs designed for screen printing of solder paste will have much less space between pads, and so, the amount of surface mount adhesives dispensed will have to be carefully dictated to maintain application integrity. In such a scenario, you might have to make use of custom designed nozzles to control adhesive dispensing.

The above parameters should provide you with all the info necessary to perfect your surface mount adhesive application process for your PCB assembly. Hope this information will help you in handling your operations.

Alpha Assembly Solutions Inc. is the global leader in the development, manufacturing and sales of innovative specialty materials used in a wide range of industry segments, including electronics assembly, power electronics, die attach, LED lighting.