Surface Mount Technology vs. Through Hole Mount Technology

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Electronics Manufacturing Quality Control

Prior to surface mount technology (SMT) being available, electronic components were placed on boards with what is now referred to as through hole mounting (THM). This was done either by soldering the components to a PCB or by using wire wrap mounting techniques.  There are however times where though-hole components should still be used.

Benefits of Surface Mount Technology (SMT)

Surface mount technology has evolved from just a more cost effective way to install electronic components to a source of power reduction and many other benefits, including:

  • Smaller devices – without the mechanical need for leads to solder, the footprint of components can be reduced, which adds up to smaller overall end product. Ball grid arrays (BGAs) which have their leads soldered underneath them allows even smaller electronics. As an example, think of a cellular phone. When they were first introduced, they were large awkward devices – now their size is usually defined by the size of the screen and can even fit on the face of a watch. The technology has been revolutionary with the entire IoT industry.
  • Lower power requirements – leaded components used in through hole components require some bulk in order to manufacture them. This bulk leads to unnecessary power dissipation. The mechanical characteristics allow surface mounted components to be very small which minimizes this power dissipation. Also, it allows for BGAs which reduces the requirements for trace lengths in integrated circuits as the leads can be soldered under the component. Referring to the cellular phone again, early phones required auto power or small suitcases with batteries to run, current phones have self-contained batteries.
  • More cost effective – this is a major benefit of SMT. The component’s package size is generally standardized and typically placed using pick and place automation. The labor required is significantly reduced, requiring only SMT operators and maintenance.
  • Fewer errors or rework – prior to SMT, all components were hand placed. This required operators to manually choose and place each component one at a time. Once built, the unit would need to be tested, and it was often found that an incorrect component was installed or improperly soldered. With SMT, the component placement is very consistent because it essentially eliminates human error. Even when something goes wrong, it is usually the same error on all circuit boards and once found can be fixed on all boards, and corrected, in the SMT process.
  • Advanced technology – the smaller size and power requirements have led to the building of advanced devices, which would not have been possible prior to SMT. Again, think of the IoT revolution.

There is Still a Need for Through Hole Technology

While SMT has revolutionized the electronics business, there are still a few circumstances where through hole technology is preferred, including:

  • Connectors accessible to users or which require strain relief – connectors typically experience stress and require strain relief to avoid damage. SMT components are applied to a trace layer on the surface of the circuit card, which is typically not sufficient. At times, this strain relief can be provided mechanically by an enclosure. Using through hole connectors provides strain relief by utilizing the entire thickness of the board as a mechanical foundation.
  • Bulky or heavy components – components that have mass to them also require strain relief for reliability. In equipment subject to vibration or motion, the SMT trace may not be sufficient to hold a bulky component in place and may cause it to come off and damage the trace. Similar to connectors, this can be helped by using through hole components, utilizing the entire board thickness as strain relief.

While through hole technology requires some manual steps, it can either be hand soldered or wave soldered (automated process of applying solder to through hole components). A hybrid board containing primarily SMT components with required through hole components is very common.

Considerations When Upgrading Older Technology

Many older electronics use exclusively through hole components, primarily because that was all that was available at the time. Many of these have obsolete components that need to be redesigned for component availability. Assuming the requirements are the same, once the obsolete components are replaced, the remaining components should be evaluated to see if they can be replaced with SMT components. Often an exact replacement is available in SMT. Changing over to SMT where possible and keeping required through hole components will realize many of the benefits of SMT including lower cost, better reliability, and lower power requirements.

Partner with an Electronics Manufacturing Expert

ACDi has extensive experience with SMT and through hole and can help with all aspects of the technologies, including redesigning for SMT, PCB layout, and providing tips for more efficient SMT manufacture. Contact us to help you determine the best technology for your electronic device manufacturing.









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