One of the on-going challenges contract electronics manufacturers (CEMs) face is the demand to reliably produce increasingly complex product assemblies.
Often the printed circuit board assemblies (PCBAs) contained within these products require components to be placed on both the top and bottom side of the circuit board. As a result, the CEM has to pass the PCBA through the reflow process twice – relying on the magic of surface tension to not let them down – literally.
When relatively small and light electronic components feature on the bottom side of a board this process isn’t usually a problem but what about when there are much larger and heavier parts? Well, usually the CEM has to carry out another process using adhesive dots or "glue" to ensure the components are firmly held in place while the PCBA is passed through the reflow oven for the second time.
In this blog post, we will look at the different ways this process can be carried out and a make a quick time and cost comparison between both.
In simple terms, there are two different ways to apply relatively small amounts of adhesive: by hand using a cartridge/syringe solution; or through an automated process requiring a piece of specialist equipment.
Dispensing adhesive by hand
Unsurprisingly, dispensing adhesive by hand is a relatively low-cost option - although it can be time-consuming if there are a large number of devices that require attention, or the batch size is relatively high. While this method is perfectly adequate for small production runs it does rely on an operator’s consistency between each board and, therefore, the reliability of the overall process can sometimes be called into question.
To understand the timings and cost involved in dispensing adhesive by hand, let’s look at a case study example, which includes:
- A densely populated double-sided board with heavy surface mount (SMT) components on both sides.
- x9 heavy components (inductors) on the underside of the board; requiring x2 adhesive dots per component.
- Ordered in batches of 400.
- Therefore requiring a total of 7,200 adhesive dots across the batch.
In this scenario, each PCBA is removed from the SMT line and taken to a dedicated gluing area for approximately three minutes, in order to apply the adhesive. If we assume the production equipment carries an operating cost somewhere in the region of £100 per hour, then this manual work represents 20 hours of time and, therefore, (assuming the SMT line stands idle until the PCBAs return from the gluing process) up to £2000 of cost.
So how does this compare with an automated solution?
Dispensing adhesive by machine
A number of manufacturers now offer automated solutions for dispensing small amounts of adhesives - like DEK and their "Stinger" integrated dispense module. This optional extra is designed to dispense adhesive dots or additive solder paste onto a PCB sequentially after the print cycle. The module is integrated into the printer and consists of three key components: the module hardware itself, controller and operating software.
Not only is the accuracy of the adhesive placement improved, providing the printer cycle time is longer than the placement time of the slowest machine, but the Stinger dispenses the adhesive at no extra time or cost. The other obvious benefit for CEMs investing in this kind of automated solution is they are not restricted when it comes to medium or larger batches.
An automated dispense module can cost in the region of £10k-£12k. However, providing the CEM is building a number of different boards requiring this process or has an on-going demand to build in medium volumes, it is easy to see how this would soon end up paying for itself when compared to the manual case study above.
It’s worth mentioning here that a number of larger "in-line" dispensing systems are also available. These tend to offer higher process speeds, tighter tolerances and the ability to vary the size, shape and depth of any adhesive applied. They also come with a much larger price tag: four to five times that of an integrated module solution in some cases. So, unless the CEM is confident they have the required level of throughput to see a return, they are unlikely to add one to their equipment lists.
There you have it. A quick time and cost comparison between the manual and automated dispensing options to help overcome the challenges of double-sided PCBA within electronics manufacturing. While the name Stinger may conjure up images of bees, wasps, car chases or military hardware, CEMs investing in such a solution can help ensure their customers don’t get stung with poor quality PCBAs or nasty rework costs.
Image by Steve Snodgrass
