Assembly by Hand vs. Machine Assembly

Nearly every successful company passes through the difficult transformation of being small to being large. As this transition occurs, there are many product development decisions to be made. For instance, in the past, it was not uncommon for smaller companies and startups to hand solder small quantities of circuit boards in order to fine-tune their PCB designs. As things ramp up and production increased, however, it made sense move to automated machine assembly. Today, it is possible to affordable machine-assemble boards regardless of the product lifecycle phase. In fact, companies exist that specialize in machine assembling low-volume and prototype orders—even for just one or two boards.

With individual hand-solder joints, achieving consistent quality in large volumes can be difficult. Before pick-and-place machines, the industry suffered from variable quality, as operators tirelessly soldered thousands of solder joints a day. The hand-assembly process with human fallibility easily can result in incorrect part placement on a PCB. Inconsistency is a major problem with hand assembly while automatic assembly virtually eliminates misplaced components. Size constraints imposed by hand assembly are also a consideration. During the period from 1960 to 1990, the industry was only concerned with leaded resistors and through-hole chip packages. As electronics got smaller, the ability to hand solder these new parts decreased. Pick-and-place machines make it possible to properly place the new, smaller, lower cost 0402, 0201 and 01005 chips and larger, high pin count, BGA chips.

Lead-free solders are different from traditional tin/lead solder and more difficult to hand solder, as they have higher melting points and inferior wetting properties. Using a typical hand-solder iron, solder wetting will take a little longer and the solder will tend to spread less. Non-eutectic, lead-free alloys have a very small plastic range so the part being soldered must not be moved until the solder has cooled down and solidified; something that can be hard to achieve with hand placement and hand soldering. Due to this and other factors, the quality of hand soldering by even the best workers will struggle when compared to the consistency of infrared-tunnel soldered joints. The even solder joints and flat components delivered through the combination of infrared soldering reflow, properly metered solder paste, and a good quality pick-and-place machine is hard to beat.

Speed also is a major roadblock with hand soldering. A manual operator would have to work very hard to put down and solder 1000 parts an hour. A solder paste applier, high-speed chip shooter, pick-and-place machine and infrared oven placed in a conveyor configuration can apply solder paste, place and solder 50,000 parts or more per hour. While certain pick-and-place machines advertise significantly higher numbers than that, real life cases usually bring the actual specifications down. However, even at the reduced rate, pick and place machines are orders of magnitude faster than hand soldering.

To set up a small, automatic assembly line is not difficult, but can be expensive. You would need an accurate screen stencil printer and a universal type pick-and-place machine, which is designed to place the type of chips and parts that you use. You would also need a small, infrared tunnel oven and a microscope quality assurance station. You can have individual assembly units and PCB stackers to hold the PCB while in progress or you can connect all the machines together with automatic handlers and let them pass through the entire automated process without human interaction. You will probably need a few hand-repair stations as well as special hand-operated, hot-air chip soldering/de-soldering units for those parts that need some touch up. As an operator, it is important to protect the workers from health concerns. A serious problem with hand soldering is that the operator is exposed to solder fumes and flux fumes.

Small, vacuum-operated local fans can help to cut the operators’ contact with metallic compounds such as lead, copper, cadmium, bismuth, antimony and tin. Even without the lead, the exposure threat still exists with lead free solder, as the operator is handling solder rolls and components.

A properly set up assembly line only needs a few people to run; a significant savings in labor costs over hand soldering. A single automatic line can place and solder more components than 50 hand solder operators, and do it with better, more consistent quality. This increased amount of automation can bring the automated assembly costs down to the same level as hand soldering, while also experiencing a higher level of quality and repeatability. However, the most economic route for machine-assembling PCBs is to outsource the assembly to a trusted assembly partner. PCB assembly companies have invested in the equipment and processes necessary to deliver high-quality, fully assembled boards in less than a week. Leaving the assembly to the experts, will shave days, or even weeks, off your product development timeline, allowing you to bring products to market faster with higher profit margins.

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