When designing a printed circuit board for assembly, it is tempting to assume that double-sided boards (DSB) offer more value. After all, you are packing more componentry into a small space, so it must be a smarter, cheaper approach, right?
This assumption can lead designers astray. As always, the use case should drive the design and, in many cases, a single-sided board (SSB) is the smarter choice. When reducing unit cost of the PCB assembly is paramount, SSBs will cheaper every time.
SSBs have copper tracks on one side, where the Surface Mount Technology (SMT) components are placed, with through-hole components typically placed on the others side. DSBs have copper on both sides, with vias connecting the two sides, offering double the track and componentry placement options. Multi-layered boards offer even more options offset by increasing complexity.
To understand why SSBs deliver a cheaper unit cost, it is necessary to consider the whole production process.
At the start of the process, DSB and multilayered bare boards will be more expensive than a single sided board. As the space between traces narrows and more expensive preparation and tooling is required, such as laser drills, the cost will increase, particularly for low volume applications. SSB are larger than their DSB counterparts, but if your application is not space constained, it makes sense to go with a SSB.
The next step in 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. Double-sided boards need two runs through the oven. The boards need to be checked to ensure that heavy components don’t fall off the bottom on the second run, with preventative measures taken if necessary.
SSBs necessarily lend themselves to simple circuit designs with a relatively low density of components. On the other hand DSBs provide more layout flexibility for complex designs. As a general rule of thumb, SSBs are great for simple designs at high volume where space is not a constraint. For complex, lower volume designs which need to fit in a constrained space, DSB and multilayer boards may be the better option.
For more information, this article by Altium provides an interesting perspective.
Comparing SSBs to DSBs is just one of many considerations in designing and manufacturing a PCB assembly. To gain the full perspective, download our Electronics Manufacturing Checklist which outlines 44 ways to ensure seamless electronics manufacturing.