In the world of electronics, creating durable and reliable connections is critical, especially in harsh environments where high vibration, extreme temperatures, and corrosive conditions can wreak havoc on printed circuit boards (PCBs). Plated Through-Hole (PTH) design offers a proven solution for ensuring robust connections under such challenging conditions. This blog post dives deep into how PTH technology can be optimized for harsh environments, focusing on key considerations like PTH for high vibration, PTH for extreme temperature, PTH for corrosive environments, conformal coating PTH, and robust PTH design. Whether you're an engineer designing for aerospace, automotive, or industrial applications, you'll find actionable insights to enhance the reliability of your PCB assemblies.

What Is Plated Through-Hole (PTH) Technology?

Plated Through-Hole (PTH) technology involves drilling holes through a PCB and plating the inner walls of these holes with a conductive material, typically copper. This creates a reliable electrical connection between different layers of a multilayer PCB or between components mounted on the board. Unlike surface-mount technology (SMT), which relies on pads on the board's surface, PTH provides a stronger mechanical bond by allowing component leads to pass through the board and be soldered on the opposite side.

PTH is particularly valuable in harsh environments because of its durability. The mechanical strength of through-hole connections helps resist stress from vibration, while the plated copper offers a stable conductive path even under thermal expansion or contraction. Let’s explore how PTH design can be tailored to withstand specific environmental challenges.

Why PTH Is Ideal for Harsh Environments

Harsh environments expose electronics to conditions that can degrade performance or cause failure. These include mechanical stress from vibration, thermal stress from extreme temperatures, and chemical degradation from corrosive substances. PTH technology addresses these challenges in several ways:

Mechanical Stability: The physical insertion of components through the board creates a stronger bond compared to surface-mount components, making PTH ideal for high-vibration settings.
Thermal Resilience: PTH connections can better handle thermal expansion and contraction, reducing the risk of cracks or breaks in extreme temperatures.
Corrosion Resistance: With proper design and protective coatings, PTH can withstand exposure to moisture, salt, and other corrosive agents.

In the sections below, we’ll break down how to optimize PTH for high vibration, PTH for extreme temperature, and PTH for corrosive environments, along with strategies like conformal coating PTH for added protection.

Optimizing PTH for High Vibration Environments

In applications like automotive, aerospace, and industrial machinery, PCBs are often subjected to constant or intense vibration. Vibration can loosen connections, crack solder joints, or cause components to detach. PTH for high vibration environments offers a robust solution due to its mechanical strength.

When designing PTH for high-vibration settings, consider the following:

Hole Size and Component Fit: Ensure the drilled holes are sized precisely to match component leads. A tight fit reduces movement during vibration. For example, a hole diameter tolerance of ±0.05 mm can significantly improve stability.
Solder Joint Quality: Use high-quality solder with a melting point suited to the operating environment. A well-formed solder fillet around the PTH connection distributes stress evenly, reducing the risk of cracks.
Board Thickness: Thicker PCBs (e.g., 2.0 mm or more) provide better resistance to bending and flexing under vibration. This is especially important for multilayer boards with multiple PTH connections.
Component Selection: Opt for components with robust leads that can withstand mechanical stress. For instance, using through-hole resistors with a power rating of 1W or higher can ensure durability.

PTH connection on PCB during high-vibration testing for durability

Designing PTH for Extreme Temperature Conditions

Extreme temperatures, whether scorching heat or freezing cold, can cause materials to expand or contract, leading to stress on PCB connections. PTH for extreme temperature environments must account for thermal expansion differences between the board material, copper plating, and solder.

Here are key strategies to ensure reliability:

Material Selection: Choose PCB substrates with low coefficients of thermal expansion (CTE), such as FR-4 with a CTE of around 14-17 ppm/°C. Match this with copper plating that has a similar CTE to minimize stress at the PTH barrel.
Plating Thickness: Thicker copper plating inside the through-hole (e.g., 25-30 micrometers) can better withstand thermal cycling, preventing cracks or delamination.
Solder Type: Use solders with a wide operating temperature range, such as lead-free solders with melting points above 217°C, to maintain integrity in high-heat conditions.
Thermal Relief Pads: Incorporate thermal relief designs around PTH pads to reduce heat buildup during soldering and operation, preventing damage to the plated barrel.

For extreme cold, ensure that the solder and plating materials remain ductile at low temperatures (e.g., below -40°C) to avoid brittleness and cracking. Testing PTH designs under thermal shock conditions, such as cycling between -55°C and 125°C, can validate their performance.

PCB with PTH connections under extreme temperature testing

Protecting PTH in Corrosive Environments

Corrosive environments, such as those with high humidity, saltwater exposure, or chemical vapors, pose a significant threat to PCB reliability. PTH for corrosive environments requires protective measures to prevent oxidation and degradation of the copper plating and solder joints.

Consider these design and manufacturing tips:

Surface Finish: Apply a corrosion-resistant surface finish, such as immersion gold or silver over the copper plating, to protect exposed areas of the PTH. These finishes can resist tarnishing even in humid conditions with up to 95% relative humidity.
Sealing Techniques: Use sealants or potting compounds around PTH connections to block moisture ingress. Silicone-based sealants, for instance, offer excellent resistance to water and chemicals.
Board Layout: Position PTH connections away from board edges or areas prone to moisture accumulation to reduce exposure to corrosive agents.

One of the most effective ways to shield PTH in corrosive settings is through the use of protective coatings, which we’ll explore in the next section.

Enhancing Protection with Conformal Coating PTH

Conformal coating PTH involves applying a thin polymeric film over the PCB to shield it from environmental factors like moisture, dust, and chemicals. This coating conforms to the irregular shape of the board, covering PTH connections and preventing corrosion or electrical shorts.

Here’s how conformal coating enhances PTH reliability:

Moisture Barrier: Coatings like acrylic or silicone create a barrier against water and humidity, which is crucial in marine or tropical environments.
Chemical Resistance: Urethane coatings can protect against harsh chemicals, making them suitable for industrial applications where exposure to solvents or acids is common.
Thermal and Vibration Dampening: Certain coatings, such as parylene, provide additional thermal insulation and vibration dampening, supporting PTH performance in combined harsh conditions.

When applying conformal coating, ensure that it penetrates around the PTH connections without clogging the holes. Techniques like selective coating or dip coating can achieve uniform coverage. The coating thickness typically ranges from 25 to 250 micrometers, depending on the level of protection needed. Always test the coated PCB under simulated environmental conditions to confirm that the coating adheres well and doesn’t interfere with electrical performance.

PCB with conformal coating protecting PTH connections in harsh environments

Key Principles of Robust PTH Design

Creating a robust PTH design requires a holistic approach that combines material selection, manufacturing precision, and environmental protection. Here are the core principles to follow:

Barrel Integrity: Ensure the copper plating inside the through-hole is uniform and free of voids or defects. A barrel thickness of at least 20 micrometers is recommended for most harsh environment applications.
Annular Ring Size: Design the annular ring (the copper pad around the hole) with sufficient width, typically 0.25 mm or more, to provide a strong soldering area and resist mechanical stress.
Drilling Precision: Use high-precision drilling equipment to avoid rough edges or misalignment, which can weaken the PTH connection. A drill bit tolerance of ±0.025 mm ensures accuracy.
Testing and Validation: Perform rigorous testing, such as microsection analysis, to inspect the PTH barrel for cracks or plating inconsistencies. Environmental stress testing, including vibration, thermal cycling, and salt spray tests, can confirm the design’s durability.

By adhering to these principles, you can create PTH designs that stand up to the toughest conditions, ensuring long-term reliability for critical applications.

Applications of PTH in Harsh Environments

PTH technology is widely used in industries where reliability under harsh conditions is non-negotiable. Some key applications include:

Aerospace: PCBs in satellites and aircraft must endure high vibration during launch and extreme temperature fluctuations in space. PTH ensures stable connections for critical systems.
Automotive: In vehicles, electronics face vibration from rough terrain and temperature swings from engine heat to winter cold. PTH is often used for power modules and control units.
Marine: Equipment on ships or offshore platforms is exposed to saltwater and humidity. PTH with conformal coatings protects against corrosion.
Industrial: Factory automation systems operate in environments with dust, chemicals, and mechanical stress. Robust PTH designs ensure uninterrupted performance.

Conclusion: Building Reliability with PTH Design

Plated Through-Hole (PTH) technology remains a cornerstone of reliable PCB design, especially in harsh environments where high vibration, extreme temperatures, and corrosive conditions threaten performance. By optimizing PTH for high vibration, PTH for extreme temperature, and PTH for corrosive environments, and by leveraging techniques like conformal coating PTH, engineers can create robust PTH designs that stand the test of time. From precise hole sizing and material selection to protective coatings and rigorous testing, every detail matters in ensuring robust connections.

At ALLPCB, we’re committed to supporting your projects with high-quality PCB manufacturing solutions tailored to harsh environment challenges. Whether you’re designing for aerospace, automotive, or industrial applications, our expertise in PTH technology can help you achieve unmatched reliability. Explore our services to see how we can bring your designs to life with precision and durability.