Achieving both yield and cost by switching between through-hole and via-in-pad

Understanding Through-Hole and Via-In-Pad

When it comes to printed circuit board (PCB) design, choosing the right method for connecting layers is crucial.
Two popular techniques that engineers often consider are through-hole and via-in-pad.

Both have unique advantages and drawbacks, especially when balancing cost and yield, the number of successful units produced over the total units attempted.
Understanding these concepts can help you make informed decisions that enhance both efficiency and functionality in your PCB projects.

What is Through-Hole Technology?

Through-hole technology (THT) is a mounting scheme in PCBs used where component leads are placed into holes drilled into a PCB.
These leads are then soldered either to pads on the opposite side or in a single layer board, on the same side.

This technique is well-known for its reliability due to the strong mechanical bond it can create.
It is particularly suitable for components that will experience mechanical stress, such as connectors or larger, heavier components.

What is Via-In-Pad Technology?

Via-in-pad technology involves placing vias directly beneath or within a component’s pad.
This method can conserve space on the PCB, allowing for more compact and efficient designs.
It is particularly effective in high-density interconnect (HDI) boards or when working with smaller, more complex components like Ball Grid Arrays (BGAs).

Via-in-pad can improve the thermal and electrical performance of a board by providing shorter and more direct paths for signals and heat.

Cost Considerations: Through-Hole vs. Via-In-Pad

When it comes to cost, through-hole and via-in-pad technologies have distinct implications.
Through-hole processing tends to be more expensive due to the additional steps required in manual assembly and the increased PCB real estate that these components consume.
However, it generally provides a better yield in terms of physical resilience and reliability.

Conversely, via-in-pad can reduce the material cost by allowing for smaller boards and less copper usage.
Despite its space-saving advantages, it may require more sophisticated manufacturing processes, potentially leading to higher initial production expenses.

Reducing Costs with Design Optimization

To find a balance between yield and cost, it is important to optimize your PCB design.
Employing a mix of through-hole and via-in-pad can help achieve this.
For instance, using through-hole processes for high-stress components ensures durability, while via-in-pad can be applied for signal integrity in densely packed areas.
Designers can significantly reduce manufacturing costs by leveraging software tools capable of simulating these scenarios.

Yield Considerations: Balancing Functionality and Durability

Achieving a high yield is essential for both the profitability and the sustainability of PCB production.
The yield is influenced by both the strategies used and the components selected.

Benefits of Through-Hole for Reliability

Through-hole technology boasts a historical advantage in terms of yield when mechanical strength is required.
Because the component lead extends entirely through the board and is soldered in layers, this ensures a robust connection that is less susceptible to mechanical failure.
This is why it remains in use for applications where durability is a primary concern, such as aerospace and automotive industries.

Leveraging Via-In-Pad for Signal Integrity

For applications where signal integrity and precision are crucial, via-in-pad offers a compelling advantage by reducing inductance and resistance when signal paths need to be short and direct.
This reduces the probability of signal loss or delay, thus improving the overall yield of the electronic device being manufactured.
Via-in-pad technology also reduces the incidence of cold solder joints and other defects that might arise from inadequate heat distribution during soldering.

Switching Between Technologies to Optimize Performance

By carefully evaluating the needs of the PCB project, you can decide where to best implement through-hole or via-in-pad technology.
In practice, a hybrid approach often makes sense.

For instance, strategically using through-hole for power and ground connections can support a solid structure and reliability.
Meanwhile, you can reserve via-in-pad for accommodating small signal connections or high-speed data paths.

Steps to Enhance Design Flexibility

1. **Evaluate Your Application’s Needs:** Consider what the finished product will be used for, its environmental conditions, and performance expectations.

2. **Plan for PCB Layout Optimization:** Use design software that allows for easy swapping between through-hole and via-in-pad based on functionality requirements.

3. **Prototype and Test Early:** Generate prototypes early in the design phase to test both mechanical and electrical integrity and iterate upon feedback.

4. **Review Manufacturing Capabilities:** Align your design choices with your manufacturer’s capabilities and limitations, which can contribute significantly to yield and cost considerations.

5. **Keep Open to Updates:** With technological advancements, be prepared to adapt your design strategies to incorporate new tools or methodologies for achieving an optimal balance.

Conclusion

In summary, the decision between through-hole and via-in-pad technology is not one that is clear-cut.
Instead, it requires a comprehensive understanding of each method’s strengths and limitations relative to your specific PCB application.
By strategically applying these technologies, balancing cost and yield becomes achievable, which ultimately contributes to successful and cost-effective electronics production.