While many designs have shifted toward surface mount, through-hole assembly remains a strategic choice in the right applications. Understanding when and why to use it is key to making the best design decision. The reality is that through-hole component solder joints are typically more robust for applications where stress will be frequently applied to that component.
The basic difference in through-hole vs. surface mount technology (SMT) components is in mounting techniques and applications. For example, through-hole connectors are inserted through drilled and/or plated holes in the PCB and then soldered on the opposite side of the board, making them ideal for applications where cables or subassembly (daughter) boards are frequently plugged and unplugged. SMT connectors are soldered to pads on the PCB. They are better suited to applications where cables or subassemblies are connected during assembly and aren't plugged and unplugged in normal applications.
| Through-hole | SMT | |
|---|---|---|
| Mounting | Inserted through drilled and/or plated holes in the PCB and soldered on the opposite side of the board | Soldered to pads on the PCB |
| Best for | Applications where cables or subassembly (daughter) boards are frequently plugged and unplugged | Applications where cables or subassemblies are connected during assembly and aren't plugged and unplugged in normal applications |
| Assembly process | Placed manually in a secondary assembly process following reflow, then hand-soldered or run through a wave or selective soldering process | Placed as part of an automated assembly process and then reflowed |
Through-hole connectors are typically more costly than their SMT counterparts because they add additional steps to the assembly process. For example, in the SMT assembly process, connectors are typically placed as part of an automated assembly process and then reflowed. When through-hole connectors are used, they are placed manually in a secondary assembly process following reflow, and either hand-soldered or run through a wave or selective soldering process. Wave soldering requires fixturing, which can add several hundred dollars in non-recurring tooling costs. Selective and wave solder also have quality implications as the printed circuit board assembly (PCBA) goes through an extra thermal cycle.
For products subject to shock and vibration, products that carry current, or products where field repair or modifications will require cables or subassemblies to be frequently plugged and unplugged, through-hole connectors provide the most robust solder joint connection. Military connectors typically require through-hole, and motherboards with multiple USB connectors would use through-hole connectors.
For products where connectors are only accessed during initial assembly, SMT connectors are typically the most cost-effective option. In cases where SMT is preferred, such as small footprint consumer products, hybrid connectors may be used. For example, USB-C connectors have through-hole leads to provide support. Staking around the connector can also be done to provide added support if a customer may be plugging a connection in and out, but this adds a process step and associated cost. If an SMT connector has a form factor that allows significant interconnection, solder joint strength will be less of a concern. For example, the Molex solder-charged C-ray connector SMT has over 100 connections. Lead shape can also matter with SMT connectors. Flat-leaded SMT connectors typically perform better than J-leaded connectors.
When SMT connectors are reflowed, selecting a component with a guided pin option can ensure the connector doesn't tilt or shift during reflow.
Making the right choice of connectors is highly dependent on application, operating environment, cost, and reliability goals. The team at Screaming Circuits is here and ready to help answer your questions on SMT vs through-hole component selection. Contact us at: Sales@ScreamingCircuits.com