For decades, the electronics industry depended on gold for wire bonding. The metal’s softness and oxidation resistance made it easy to manipulate, and very fine bonds could be made without cracking or damaging boards. Temperature cycling was never a major concern – a boon for automotive applications routinely exposed to harsh environments.
However, the steady and dramatic increase in gold prices – from $300-400/Troy ounce in the 1990s and early 2000s to about $1,300/Troy ounce today – made it cost prohibitive for continued use in the competitive automotive industry.
Copper wire offers a plentiful, lower-cost alternative to gold, but it is not as easy as simply replacing the gold wire bonds with copper. Replacing this component comes with unique obstacles that need to be addressed.
The primary argument in support of copper bond wire over its gold counterpart is price.
Although copper wire bonding equipment costs more than that for gold wire and throughput is measurably slower, the wire price disparity more than makes up for it.
As another positive, copper has better electrical and thermal conductivity than gold. For automotive applications, its reported 46% higher current carrying capability results in electrical/electronic (E/E) performance improvements that are almost as advantageous as the cost savings.
These benefits, though, don’t necessarily equate to value. Copper wire bonds (Cu-WBs) come with their own set of challenges, both in general and specific to the automotive industry.
Cu-WBs were first used in lower-end consumer electronics. Through continual refinement, they advanced to higher-end devices and relatively recently (2011) has become the material of choice over gold wire bonds in automotive electronics.
The evolution of Cu-WBs holds promise, but there is still much to be learned about their capabilities under harsh environmental conditions, factoring the elemental differences such as copper being harder than gold and more prone to oxidation and wire fracture. Other disadvantages include:
- Copper bond wire has a short shelf life, and must be used within one week of opening the package.
- Cu-WBs tend to corrode and separate when exposed to extreme humidity and temperatures – both of which commonly exist in automotive environments.
- Cu-WBs performance can be inconsistent over time as equipment wears.
In 2014, there was a record number of automobile recalls due, in large part, to the failure of Automotive Electronic Council (AEC)-approved “automotive grade” components. It was discovered that AEC standards did not encompass copper wire bonded ICs and although the components and the modules passed reliability and safety testing before being produced, there were still issues that arose after years of wear.
In response, the AEC is developing new automotive industry specifications to be used when qualifying components that contain copper wire. Validation testing is incumbent upon OEMs to comply with the standards and avoid a repeat of expensive recall repercussions.
Component-level Thermal Cycle Tests
OEMs expect robust E/E components that will pass module level testing, and want component-level issues resolved in testing before the modular stage, when time and cost investment is minimal.
To that end, efforts are underway to develop ways of consistently validating reliable components and resolving any weaknesses at the component testing level. Component-level Thermal Cycle Tests are performed using loose components and assess the stresses generated within the component, before the modular testing phase.
With the added pressure on OEM’s to have validation testing on the modular level run smoothly, some are suggesting that suppliers run existing component-level thermal cycle tests three times as opposed to the AEC-required one time. The fact remains that if components aren’t reliable, budget and timeline issues arise and OEMs are left with little recourse but to start the expensive design-test-build-fix (DTBF) process over again.
Physics of Failure (PoF)
There is a better way to successfully incorporate Cu-WBs. Computer-aided engineering (CAE) is empowering automotive manufacturers with the ability to cut test time and costs by using software for reliability testing that requires no physical prototyping.
DfR Solutions’ Sherlock Automated Design Analysis™ software is one such tool. Sherlock leverages Physics of Failure (PoF) to provide automotive manufacturers with access to virtual design and testing that:
- Predicts reliability over the automotive lifespan of 10-15 years by factoring in demanding environmental challenges (temperature, vibration, shock, etc.).
- Tests components before the module testing stage to keep OEM timelines and budgets on track while simultaneously assuring compliance with stringent new vehicular safety requirements to avoid recalls.
- Makes the transition to copper wire bonds easier through a deep knowledge and understanding of the processes and mechanisms that induce failure in order to improve product performance.
Cu-WBs offer financial advantages that are imperative in the competitive automotive industry, as long as OEMs have time- and cost-efficient ways to ensure reliability. Contact us today to learn how Sherlock can work for you!