PCB experts usually agree that automated processes reduce errors during assembly. Modern surface mount technology allows SMT line machines to produce better results more consistently for the broad majority of PCB components.
However, there are times when assembling a PCB by hand makes sense. In particular, when building prototype circuit boards in low quantities, the right combination of factors may make manual PCB assembly the preferred option.
One of the primary factors making a case for hand assembly is volume. Any order above ten individual boards is best performed through automated pick-and-place assembly. However, there are plenty of instances when manufacturers don’t need more than ten PCBs. If a manufacturer is deciding between two main prototype designs, it may only need two boards to fulfill its objective.
In this case, having an employee load and solder components onto the circuit board can be advantageous in terms of man-hours spent. Calibrating an SMT machine for such a job may take longer and present more complications than simply assembling the pieces manually.
Another factor that may go into the decision to assemble a prototype PCB order by hand is component choice. Components made of low-melting point metals may not withstand the heat of automated soldering without careful and painstaking machine calibration, for instance.
Similarly, a component with an unusual shape and center of gravity may present issues during automated processes that, for low-volume orders, are best addressed by a skilled technician’s hand. Also, sometimes manufacturers send parts in bulk or in loose bags that can’t be placed on SMT line machines, or simply send insufficient documentation for an automated process to make sense.
If the required volume is low, the board technology is simple, and there are relatively few individual components per-board, a professional prototype PCB assembly service may choose to build the board by hand.
Naturally, hand assembly produces a larger margin of error than automated PCB assembly. This is one of the main reasons people use large-volume machines in the first place. However, having a well-defined manual workflow and numerous quality failsafe checks ensures that the finished board functions just like an automated one would.
For instance, there is little reason not to automate the solder paste printing process. Screen printing solder paste onto the circuit board ensures consistent results and takes less time than manually applying paste even for small-volume orders.
For best results, the manual element should only consist of the actual placement of components on the board. The result is easy to verify using standard process and quality checks, ensuring that low-volume PCB orders are subject to the same standards as automated high-volume ones.