The nirvana of modern electronics manufacturing is to design a printed circuit board (PCB) assembly with minimal labour input. Over the past decade, electronics manufacturers such as Circuitwise have been investing in state-of-the-art high-speed pick and place machines, that is bringing this vision to life. With smart design, it is now possible to manufacture PCB assemblies in Australia at a cost which is competitive with any Asian manufacturer.
Following are our key recommendations for designers of PCB assemblies to optimise your design for manufacture:
1. Put all SMT components on one side
2. Put the heavy components on one side
3. Minimise through-hole components
A major cost component for electronics assembly is setting up the SMT machines before a run. Set up includes kitting up, verifying you have all the right components, programming the machines, and first article inspection. Putting all your SMT components on one side means this process only has to be done once. The same principle applies when putting the boards through the reflow ovens.
If you do need a two-sided board, putting all your heavy components on just one side also smooths the production process. If heavy components are on both sides, then when the board goes through the reflow oven a second time, a heavy component will be hanging off the bottom. To prevent it from falling off, the component needs to be glued in place, which adds cost to the process.
In the past, many components were only available as through-hole components, but that is no longer the case. SMT components are cheaper, faster to assemble and do not involve manual labour to prepare and place them. However, some designers are reluctant to move away from old proven designs that needlessly specify a through-hole component when newer SMT components are available. If you are producing large volumes of PCB assemblies, it is certainly worth considering a redesign if you have unnecessary through-hole components.
For new designs, investigate all options for avoiding through-hole components and generally minimise their number. It is also possible to use some through-hole components on the SMT lines. It is worth talking to your manufacturer about options for replacing older styles of through-hole with SMT machine-friendly versions.
For the remaining through-hole components, the aim should be to make the soldering process as efficient as possible. The most efficient process for soldering through-hole components is wave soldering, which works well if your board is one-sided. However, wave soldering is problematic for two-sided assemblies. Unprotected SMT components fall off in a solder wave. So a protective pallet needs to be created to expose only the through-hole components to the wave. Creating a pallet is a relatively expensive step that is generally only cost-effective for large volume or very high-value products.
The next most efficient process for two-sided boards is selective soldering. To optimise a design for selective soldering, make sure you leave adequate clearance for the solder fountain to reach the pins – the more space, the better. If other components are too close to the pins, it limits the options the manufacturer has for selective soldering of those components. Selective soldering is a relatively slow process compared to wave soldering but still faster than hand soldering.
All of these steps are designed to minimise the unit cost of your assembly. The best approach is to consult your electronics manufacturer early in the design process to discuss your emerging design. Make sure you use the prototyping stage not only to check your design is working but to gain feedback on the manufacturability of your assembly.