Why lead solder still exists in PCBA and where it’s used

Over the past two decades, electronics manufacturing has undergone a profound transformation: the shift from lead-based solder alloys to leadfree formulations, driven primarily by environmental regulations such as the European RoHS directive. The goal is clear: minimize the environmental footprint of electronics and safeguard the health of those who manufacture and recycle them.

Yet despite this sweeping change, lead solder has not vanished completely. There remain sectors where its use is not only still permitted but also technically advantageous. This persistence is not about cost savings or reluctance to adopt new technology; it stems from reliability needs, thermal performance benefits, and decades of proven long-term field data that newer alloys have not fully matched in some specific use cases.

The technical edge: why tin lead‑ solder still performs

Traditional tin lead solder, typically Sn63/Pb37, has a lower melting point of around 183 °C, reducing thermal stress on printed circuit boards and sensitive components during assembly. This is particularly valuable for complex or densely packed designs, where components might otherwise experience damage or performance drift due to high thermal loads during soldering.

Tin-lead solder also offers greater ductility, enabling solder joints to absorb vibration, thermal cycling, and mechanical shock better than many leadfree alloys. Another key advantage is its resistance to tin whisker growth, the spontaneous formation of conductive filaments that can cause shorts in pure-tin or certain leadfree finishes.

For these reasons, regulatory exemptions still allow the use of lead solder in specific sectors. Aerospace, defence, and space electronics rely on it because maintenance can be extremely difficult or even impossible, and mission failure unacceptable. The same applies in high reliability medical devices and diagnostic equipment, where stability and long-term consistency are critical for patient safety and regulatory compliance. Even certain industrial electronics depend on leaded solder when repairing legacy equipment, where metallurgical compatibility with existing lead-based assemblies is mandatory to ensure continued reliability.

Proven reliability over novelty: the role of lifetime data

There are also niche performance driven applications, such as high-end automotive motorsport, where electronic systems must withstand extreme vibration, rapid temperature cycling, and high mechanical stress, all while maintaining complete lifecycle traceability. In these cases, production runs are extremely limited and not intended for mass-market vehicles, making the continued use of proven, high reliability materials an intentional and justified choice.

Another example is found in long lifecycle energy and scientific systems—such as offshore wind turbine controls or precision laboratory instrumentation—where the electronics must deliver consistent performance for decades in challenging environments. In these applications, redesigns are infrequent and costly, and the ability to rely on decades of proven material data is often prioritized over adopting newer but less field proven alternatives.

These examples highlight another important factor: long‑term data. Many safety‑critical sectors adopt new materials cautiously, because reliability standards are built on decades of statistical performance data. Lead‑free solder technologies, although mature for consumer and most industrial markets, still lack some comparable lifetime data in specific extreme environments. In applications where failure could result in life‑threatening consequences or catastrophic financial loss, engineers often choose the known, proven path.

That said, lead‑free soldering is no longer an immature technology. Modern alloys like SAC305 have undergone extensive validation, and accelerated aging tests are now widely used to simulate long‑term reliability in a controlled lab environment. While legacy data remains a deciding factor in some industries, the gap between leaded and lead‑free solutions is increasingly narrow—and in many cases, fully bridgeable with proper design and validation procedures.

From common practice to a justified exception

So why not simply transition fully to leadfree solder? In fact, for the vast majority of industries, that transition has already taken place. Alloys such as SAC305 (tin silver copper) have become the standard for consumer electronics and most industrial electronics, offering good performance for general purpose applications.

But for safety critical sectors with exceptionally long validation cycles and product lifespans, there is still an element of uncertainty: how will these newer leadfree alloys behave after decades of thermal cycling, vibration, and environmental exposure? That unknown, combined with the reduced thermal stress offered by lead solder during assembly, has kept it relevant in areas where absolute reliability outweighs regulatory simplicity.

Today, the use of lead solder in PCBA is no longer a default manufacturing practice—it is a deliberate, carefully considered engineering decision, made only when safety, reliability, and compatibility with legacy systems demand it. As leadfree technologies evolve and long-term performance data accumulates, exemptions are reviewed regularly and are expected to continue shrinking.

But for now, lead solder maintains a small yet critical role in ensuring reliability where failure simply is not an option.