PCBA: What is Through-Hole Assembly & Surface Mount Assembly!

Printed circuit boards or PCBs provide the foundation for a significant amount of the technology that we use every day. From computers and smartphones to appliances and vehicles, PCBs enable complex electronic circuits and components to be compact and reliably connected. The process of assembling the components onto the PCBs during manufacturing is known as PCB assembly or PCBA.

There are several key steps and processes involved in assembling a PCB. First, the PCB is designed and fabricated, consisting of conductive copper traces and pads on an insulating base substrate. Components must then be precisely placed and mounted onto the PCB. This is accomplished through two main techniques: through-hole assembly or surface mount assembly. Additional processes like soldering, cleaning, inspection, and testing ensure the quality and reliability of the final assembled PCB.

What are the common PCBA processes used in the market?

Through-Hole Assembly

Through-hole assembly, also known as through-hole technology (THT), is a method of mechanically assembling electronic components into printed circuit boards (PCBs). In through-hole assembly, component leads are inserted into holes drilled in the PCB and soldered to pads on the opposite side to create both mechanical and electrical connections.

The through-hole assembly process typically involves the following steps:

- PCB Fabrication - The PCB is designed and fabricated with plated through-holes at locations where components will be placed. The holes are plated with a conductive material to enable soldering.

- Component Insertion - Components are inserted into their corresponding holes on the PCB. Discrete components like resistors and capacitors are often inserted by automated machines, while integrated circuits are inserted manually.

- Soldering - The component leads protruding through the PCB are soldered, usually by wave soldering. Molten solder in the wave bonds with the plating in the holes and component leads to form solid solder joints.

- Cleaning - Any residual flux or other contaminants are cleaned from the soldered board using methods like spraying or immersion.

- Inspection - The solder joints and component placement are visually inspected and often x-rayed to validate quality and identify any defects.

Through-hole assembly can accommodate both leaded and leadless components. It allows reliable mechanical and electrical connections, though takes up more space on the PCB compared to surface mount assembly.

Surface Mount Assembly

Surface mount technology (SMT) is an advanced assembly process where electronic components are mounted directly onto the surface of a printed circuit board (PCB). Unlike through-hole components which use holes drilled in the PCB, SMT components have solder pads or terminations on the bottom that sit directly on the board's surface.

There are several advantages of SMT over through-hole assembly:

- Components can be smaller with tighter tolerances and finer pitch. This allows for greater component density on the PCB.

- Components can be placed on both sides of the PCB. This doubles the usable area compared to single-sided through-hole boards.

- Assembly can be highly automated using pick-and-place machines, reflow ovens, and other equipment. This increases speed and reduces labor costs.

- Improved performance from smaller lead lengths between components. Components are soldered in place instead of inserted through holes.

- Easier to create double-sided or multilayer boards since holes are not required to interconnect both sides.

The transition from through-hole to SMT assembly marked a major evolution in electronics manufacturing. SMT opened the door for greater miniaturization, automation, and reliability. Nearly all modern consumer electronics rely on SMT, and it remains the dominant PCBA process today due to its versatility and advantages. Mastering SMT assembly is critical for any company involved in electronics production.