Beyond Schematics: PCB Assembler

Are you curious about what goes into creating the electronic devices we use every day? Do you want to know more about the people who make it all possible? In this series, "Beyond Schematics," we will be exploring various essential roles within the electronics industry. Today, we're taking a closer look at technicians who work at PCB assemblers.

When a bare circuit board is transferred to an assembly house, it will end up in front of a PCB assembly technician. Their job is to prepare assembly equipment, materials, and verify that all placed parts are ready to use in the assembly run. In some cases, their job is to provide rework, hand placement of parts, and hand soldering.

What Does a PCB Assembly Technician Do?

The primary job function of a PCB assembly technician is to oversee the assembly process. This involves many tasks centered around setup and monitoring of machines, running inspection equipment, and occassionally doing rework. In some cases, they are better known as process engineers as their job is to oversee the assembly process and modify it as needed.

In the past, PCB assembly was entirely manual, and if you look in some corners of the world, electronics assembly is still largely manual. Through-hole and SMD parts needed to be placed manually, soldered manually, and inspected manually. In some factories in southeast Asia, it's still common to see rows of workers manually placing and soldering components onto a circuit board. This is often the case in regions where labor costs are remain low, and the components are large enough that hand soldering is still possible.

PCB assembly technicians do a lot more than just work on the SMT line. In more modern assembly operations, a PCB assembly technician has multiple responsibilities as outlined below.

BOM Checking

Before PCB assembly begins, the assembly technician team needs to verify all parts for the PCBA have been received and that they match each line in the BOM. This is one of the most time-consuming processes involved in PCB assembly, but it is the most important step in preparing for assembly.

When an assembly job involves consigned components, it is the customer's responsibility to kit parts and supply kits to the PCB assembly facility. The PCB assembly technicians will then need to verify that all components have been received and that each part is present in the BOM. When the PCB assembly company is responsible for ordering components, the assembly technician may be responsible for preparing a components order and managing shipping of parts to an assembly facility. Once all parts have been received, the technician will need to start programming assembly equipment.

Programming the SMT Line

Once a parts kit has been received and it has been verified against the BOM, the technician can begin to program the SMT line. Using the pick-and-place data generated from the PCB layout file, the pick-and-place machine used to mount parts is programmed after loading component reals/trays into the machine. The pick-and-place machine will then place parts onto solder-covered pads before passing the board into reflow.

There are two other processes to tool on the SMT line. These are:

• Programming an automated solder dispense machine (if used)
• Programming a temperature profile for reflow soldering of SMD parts

These machines are key to placing and soldering components onto a PCB. These processes are largely automated thanks to the work of a PCB assembly technician.

Inspection and PCB Rework

After assembled boards come out of the SMT line, they will need to be inspected for defects. This is done with automated optical inspection (AOI), where a camera is used to locate solder defects. BGA, LGA, and QFN placements are checked using an X-ray inspection machine. Once defects are identified, the board is flagged for rework and is set aside for repair.

Most often, rework is just performed manually. Most inspections will uncover a small number of components that might need to be resoldered. The PCB assembly technician can then dismount the component, provide a light cleaning, and then re-mount the part solder paste and a soldering iron/heat gun.

In some cases, a BGA will need to be reworked. This is a much more involved process and it requires removing the BGA package so that it can be reballed. This requires a specialized rework station that includes a hot plate, vent, and scope to assist working with solder.

Once the BGA is removed and the landing pad area on the board is cleaned, the BGA package can go through a reballing process. For low-cost BGAs, reballing may be avoided and the part can be discarded; the replacement part will then be pulled from the attrition lot. For more expensive packages, it can make sense to reball the component and give soldering another shot. Reballing involves placing new solder balls onto the bottom side of the package by placing them in a template. Once the new solder balls have bonded to the BGA package, the BGA can be resoldered onto the PCB. An example BGA rework station is shown below.

Cleaning, Final Testing, and Packaging

After inspection and after any rework is completed, the PCBA goes through a final cleaning and packaging process before it is prepared to ship to the customer. At this stage, the PCB could also have a conformal coating applied prior to packaging.

Some of the final testing and packaging steps include:

• Power-on testing, which may involve using an automated test fixture
• Flashing, which can be performed on-the-line
• Attachment of cables or wire harnesses
• Placement of stickers or markings on the PCBA
• Mounting the PCBA into its enclosure
• Attachment of any dust protective covers or seals

The finalized assembly is then packaged for shipping. For PCBAs without an enclosure, the most common option is to place the assembly into an ESD-safe bag and packed in antistatic bubble wrap for shipping. If the board is in an enclosure, it could be packed into branded packaging, although not all assmbly companies will provide this service. Once packaged, the boards can be shipped to a customer or distributor.

Industry Trends Impacting PCB Assembly

As technology continues to advance at lightning speed, the field of PCB assembly is also experiencing significant changes. These industry trends are shaping the way PCB assemblers work and impacting their role in the manufacturing process. A major trend is miniaturization, with an ever-increasing demand for smaller, more compact electronic devices. With consumers seeking increasingly sleeker and more portable gadgets, PCB assemblers are tasked with fitting more and more intricate circuitry into tighter spaces than ever. This requires a high level of precision and expertise to ensure that all components are correctly placed and soldered. A key trend that continues to be a source of discussion and tension in the industry is automation and robotics. As companies strive for greater efficiency and cost-effectiveness, automated assembly processes have become commonplace.

Luckily advancements in machine learning and AI are revolutionizing quality control processes in PCB assembly lines. AI-powered inspection systems can quickly identify defects or errors during production, reducing human error significantly and saving enormous amounts of time.