What are Plated Through Holes?

In through-hole technology, the components are mounted on the PCB board by inserting their leads through the respective hole. These holes are called through holes since they are drilled from the top to the bottom of the board.

When using Plated Through Holes, as the name suggests, the inner wall of the holes is covered with a thin layer of Copper, which makes the entire inner hole area conductive. This conductivity benefit establishes an electrical connection between components and Copper tracks. It also enhances mechanical stability and reduces the overall resistance to support smooth current flow. The average Cu plating thickness is min 20µm.

As electronic components become more integrated and complex, the industry has started to focus more on the development of double-sided and multi-layered PCBs along with plated through holes, so that components may connect to the desired layers, whenever required.

Why Do Plated Through Holes Fail?

Cracks in the copper plating inside the hole are responsible for PTHs failure. It is also called barrel fatigue. It happens due to the difference in CTE values of the copper plating (17 ppm) and PCB board (70 ppm). A reliable PTH requires proper architecture (height (30 to 250 mil), Diameter (6 to 20 mil)), Material CTE, and plating (thickness, material). Insufficient plating thickness is caused by either insufficient current/time in the copper plating bath. IPC has prescribed IPC TR-579; Round Robin Reliability Evaluation of Small Diameter PTHs (less than 20 mil).

Test methods to Validate PTH reliability

• Modeling and simulation
• Cross-sectioning + solder float/shock
• Thermal shock testing (also thermal cycling)
• Interconnect stress testing (IST)
• Printed Board Process Capability, Quality, and Relative Reliability (PCQR2)
• Highly Accelerated Thermal Shock (HATS)

Click here to read about Non-Plated Through Holes.