engineering

Gold–aluminium intermetallic

Gold–aluminium intermetallic is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Gold–aluminium intermetallic rather than just read about it. In short: Gold–aluminium intermetallic is a type of intermetallic compound of gold and aluminium that usually forms at contacts between the two metals. Gold–aluminium intermetallics have different properties from the individual metals, such as low conductivity and high melting point depending on their composition.

Key takeaways

Gold–aluminium intermetallic belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Gold–aluminium intermetallic to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gold–aluminium intermetallic from memory before moving on to harder problems.

Reference excerpt

Gold–aluminium intermetallic is a type of intermetallic compound of gold and aluminium that usually forms at contacts between the two metals. Gold–aluminium intermetallics have different properties from the individual metals, such as low conductivity and high melting point depending on their composition. Due to the difference of density between the metals and intermetallics, the growth of the intermetallic layers causes reduction in volume, and therefore creates gaps in the metal near the interface between gold and aluminium. The production of gaps lowers the strength of the metal compound, which can cause mechanical failure at the joint, fostering the problems that the intermetallics cause in metal compounds. In microelectronics, these properties can cause problems in wire bonding. The main compounds formed are usually Au5Al2 (white plague) and AuAl2 (purple plague), both of which form at high temperatures, then Au5Al2 and AuAl2 can further react with Au to form more stable compound, Au2Al.

Properties

Au5Al2 has low electrical conductivity and relatively low melting point. Au5Al2's formation at the joint causes increase of electrical resistance, which can lead to electrical failure. Au5Al2 typically forms at 95% of Au and 5% of Al by mass, its melting point is about 575 °C (1,067 °F), which is the lowest among the major gold-aluminum intermetallic compounds. AuAl2 is a brittle bright-purple compound, with a composition of about 78.5% Au and 21.5% Al by mass. AuAl2 is the most thermally stable species of the Au–Al intermetallic compounds, with a melting point of 1,060 °C (1,940 °F) (see the Gold-aluminum phase diagram), which is similar to the melting point of pure gold. AuAl2 can react with Au, therefore is often replaced by Au2Al, a tan-colored substance, which forms at composition of 93% of Au and 7% of Al by mass. It is also a poor conductor and can cause electrical failure of the joint, which can further lead to mechanical failure.

Voiding

At lower temperatures, about 400–450 °C (752–842 °F), an interdiffusion process takes place at the junction, leading to formation of layers of different gold-aluminum intermetallic compounds with different growth rates. Gaps are formed as the denser and faster-growing layers consume the slower-growing layers. This process is known as the Kirkendall voiding, which leads to both increased electrical resistance and mechanical weakening of the wire bond. When the voids forms along the diffusion front, this process is aided by contaminants present in the lattice, and is known as the Horsting voiding, which is a similar process to the Kirkendall voiding.

Illustrations

Worked examples

Example 1 — a first encounter with Gold–aluminium intermetallic

Start with the simplest possible case. Write down what Gold–aluminium intermetallic claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Gold–aluminium intermetallic before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Gold–aluminium intermetallic ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Gold–aluminium intermetallic

In research: Gold–aluminium intermetallic appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Gold–aluminium intermetallic in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Gold–aluminium intermetallic is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminides, Corrosion, Gold, so understanding it makes those chapters shorter.
In everyday life: Look for Gold–aluminium intermetallic outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Gold–aluminium intermetallic in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gold–aluminium intermetallic means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Gold–aluminium intermetallic out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gold–aluminium intermetallic in simple terms?

Why does Gold–aluminium intermetallic matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Gold–aluminium intermetallic?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Gold–aluminium intermetallic.