About PCB Assembly

What is PCB Assembly?

PCB assemblies often consist of through-hole components that are attached to wires and surface mount devices (SMT), which then mount directly to the copper pads without the use of holes. In both surface mount soldering and thru-hole soldering, PCBA requires component leads to have satisfactory mechanical and electrical connection to the raw PCB. Sometimes a project may call for a mix of both SMT assembly and through-hole soldering.

Types of PCB Assembly

Surface Mount Assembly

Pros:

     •   SMT, which doesn’t require drilling, is less mechanically stressful than thru-hole assembly.

     •   SMT is a faster and lower cost manufacturing process than through-hole assembly.

     •   SMT is the optimal assembly method for component-rich designs and allows for more connections per component than thru-hole assembly.

Cons:

     •   SMT-assembled PCB prototypes and component repair can be more difficult than on a board assembled by through-hole soldering.

     •   SMT components are often not as high-powered or high-voltage as thru-hole components.

Through Hole Assembly

Pros:

     •   Thru-hole soldering provides stronger mechanical bonds than any other PCBA technique.

     •   Thru-hole soldering is the optimal PCBA technique for connectors, transformers, electrolytic capacitors, and other heftier circuit board components.

     •   Thru-hole soldering is considered to be the go-to process over SMT for many military or aerospace products.

Cons:

     •   Thru-hole soldering requires drilling into the bare board, which makes it a more time consuming process than SMT.

     •   Thru-hole soldering is more expensive than using SMT.

     •   Thru-hole mounting may not allow for as high a component density as SMT does.

     •   Thru-hole mounting often requires hand-soldering, which is considered to be less reliable than the reflow ovens used in surface mount PCBA.

Mixed technology (SMT and thru-hole soldering together)

Pros:

     •   This method is generally used for more complicated boards WHERE some surface mounting combined with some drilling would best suit a unique PCB layout.

Cons:

     •   PCB Assembly costs can be higher and assembly time can be longer due to PTH components.

History of PCBA

Manufacturers first developed surface-mount technology, originally called ‘planar mounting’, in the 1960s. IBM is considered to be pioneers of working with SMT, using the technology in the Saturn IB and Saturn V space crafts. SMT became widespread within the PC board manufacturing industry by the mid-1990s.
PC board components previously in thru-hole wire format were redesigned to feature small metal tabs or end caps that could be soldered directly onto the PCB surface during assembly. A significant advance in technology for PCBA, SMT components are easier to place using automated equipment and do not require the post- thru-hole solder step of clipping leads. With the introduction of surface-mount components, devices became much smaller, providing more complex circuits in tiny spaces such as phones and smart sensors. During PCB assembly, surface mount components reside on carrier tapes which feed into automated PCB assembly machines. Surface mount devices can be as little as a tenth the size of thru-hole devices, and the cost of simple devices can be as low as one-fourth of thru-hole devices. Integrated circuits generally do not have a significant advantage in price as compared to thru-hole devices because of the overhead cost of the chip.