This article explains gold embrittlement issues and how to avoid it.
Gold has long been revered in the electronics industry for its exceptional properties. Its resistance to corrosion, high electrical conductivity, durability, and heat resistance make it an ideal choice for various applications. Particularly, gold performs remarkably well in environments characterized by high humidity, extreme temperatures, and frequent temperature fluctuations. It is also suitable for components subjected to high cycle counts, provided the plating thickness is correctly managed.
The Downside: Gold Embrittlement
Despite its advantages, gold is not without its challenges. Its high cost is a significant consideration, and if the plating is too thin, it can become porous. Conversely, when gold plating is too thick, it can lead to a critical issue known as gold embrittlement in solder joints.
What is Gold Embrittlement?
Gold embrittlement occurs when gold from a contact mixes with tin or tin-lead solder, and the gold content exceeds 3% of the total solder weight. This threshold diminishes the ductility of the solder joint, making it vulnerable to weakness under thermal cycling. Over time, these weakened joints can lead to system failures.
Preventing Gold Embrittlement
Understanding that not all gold plating causes embrittlement is key. Typically, gold plating thickness below 20-30 µin does not present significant issues. Ideally, maintaining the contact area plating below 10 µin minimizes the risk.
Effective Strategies:
- Avoid Gold in the Tail Area: The simplest prevention method is to eliminate gold from the tail area of the contact where it connects to the board.
- Selective Gold Plating: Companies like Samtec offer selective gold plating—applying gold only in the contact area while using tin or tin-lead on the tails. This approach balances performance and reliability.
- Solder Dipping: Regardless of the initial plating style, solder dipping (tin dipping) can remove gold from the tails and coat them with a durable solder layer. This method is particularly prevalent in military and aerospace industries.
Final Thoughts
Should you be concerned about gold embrittlement? Absolutely. Monitoring the thickness of gold on contact tails is crucial. By implementing selective plating or post-plating treatments, you can maximize the benefits of gold without compromising the integrity of your solder joints.
