When to Switch From Manual to Automated Assembly

It might be surprising to hear this, but some contract PCB assembly houses still do things manually rather than setting up an automated assembly line. Those stock photos you see online with people hunched over circuit boards assembling parts: those photos are not relics of the 1990s. In some parts of the world, the lower cost of labor and lack of access to investment capital drive some assembly companies to use manual PCB assembly lines.

As long as there are proper inspection and quality control measures, as well as cleaning post-assembly, manual assembly can still be a perfectly fine option. In some cases, you have specific parts that are manually assembled with the rest of the board put through reflow, especially if you have small SMD or leadless components. But if you start to look around the world, you might find that it makes sense to move away from a manual PCB assembly house and instead use a contract manufacturer that automates most of the process.

When to Move Away From Manual PCB Assembly

Areas of the world with low labor costs and a reasonably skilled workforce are the types of places where you will find manual assembly of PCBs. Manual assembly is just like it sounds: you have rows of workers on assembly lines manually placing and soldering parts with soldering irons or heat guns.

In some parts of the world, these operations are very crude and are not the ideal facilities for assembling high-quality electronics. Still, when there is a promise of providing a competitive price on a high value contract, low-cost shops might try to get a piece of the action.

When it comes to low-cost PCB manufacturing and assembly, you usually get what you pay for. With low-cost manual assembly, that means there will be limitations on what can be assembled and the level of quality they can guarantee, if they provide a guarantee at all. With manual assembly there will be limits on what types of components can be assembled onto the PCB.

• Only larger case size passives

• No leadless components (BGAs, QFNs, or DFNs)

• Through-hole components are preferred

There are also some instances where assembly is semi-automated. In other words, portions of the process are fully automated, yet there is still high-touch from humans performing some of the work in preparation for automated assembly or inspection. The manual work done by humans could be manual placement, manual inspection, or selective assembly of specific components. For example, you may see manual placement of SMD parts, followed by reflow soldering, and then manual placement and soldering of through-hole parts.

While a fully manual or semi-automated assembly process is low cost, it's not appropriate for all products and it brings high risks of defects. Any product where quality cannot be guaranteed or there is a qualification requirement under an industry standard should probably not be manually assembled. Many of these issues are dealt with in automated assembly and inspection, and while it might mean higher cost due to payments for machine time, the additional cost translates into important benefits.

What Real Automation Looks Like

If you go to more advanced areas of the world, such as mainland China, Mexico, and fast prototyping houses in the US, companies in those regions are automating as much as possible. This is inclusive of everything in the assembly process, spanning the following areas:

• Solder application with an automated dispenser

• SMD part placement with a pick-and-place machine

• Single-sided or double-sided reflow soldering

• Wave soldering or intrusive soldering for through-hole parts

• Automated optical inspection AOI following soldering

• In-circuit testing with a flying probe machine

Companies running these facilities probably have access to additional capabilities and equipment, such as X-ray inspection for QFNs and BGAs. Additional capabilities for assembly might include thermocompression bonding for chip-on-board assemblies, or assembly with wire bonding.

The cost structure per unit of time in this assembly environment can be higher than manual assembly due to differences in labor costs and machine time charges. However, depending on the number of boards per panel and the number of assembly or inspection steps, you can have higher throughput. This translates into a shorter time to break-even for a given product, even if the production volume required for break even is higher.

The Verdict

In summary, if you're producing overseas and you want to make sure you have maximum quality, throughput, and inspection capability, only work with a contract assembler that automates their assembly process. They are more likely to catch defects, ensure high throughput, minimize rework, and deliver assembled products on time. For mass-produced consumer goods, China still remains a top option; labor costs have risen over the past decade, but so has the level of automation in Chinese factories. They can also assist with building a supply chain for consumer goods, especially when we look at non-electronic parts of a product like instruction manuals, packaging, wrapping, and shipping.

When you’re ready to prepare your product for manual or automated PCB assembly, make sure your company uses the best PCB design features in OrCAD from Cadence. If you’re ready to take even more control over net logic and board layout, you can graduate to Allegro PCB Designer for a more advanced toolset and additional simulation options for systems analysis. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity.

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