Feature: Interconnections
Plasma treatment for wire bond improvement
By Henniker Plasma design and development engineers W
ire bonding is a technique used when creating electrical inter- connections between
semiconductors, integrated circuits and silicon chips using fine wires; see Figures 1 and 2. These delicate wires carry the information to the electronic chip. If they fail, the interconnections between the electronic parts become compromised. Wire bond failure is a major concern for many semiconductor and electronics manufacturers.
Contamination threat Presence of contamination, such as bond pad and lead frame contaminations, for example, is a common cause of wire bonding failure:
Bond pad contamination Wire bond failure can occur when the fine wire bonds are unable to connect
efficiently to a bond pad. Halogen and silicone contamination can cause corrosion and impede adhesion. The formation of corrosion by-products can also become damaging, especially if present at the time of bonding.
Lead frame contamination Te lead frames used in the semiconductor device assembly process need to be completely contaminant free; see Figure 3. Contamination on the contact surfaces of lead frames can provide insufficient bond formation, which ultimately impedes adhesion, resulting in complete failure of the integrated circuit.
Plasma cleaning solutions Plasma cleaning is regarded as an industry standard for wire bonding, efficiently removing organic contaminants and thin oxide layers under high throughput conditions, quickly, efficiently and reproducibly, greatly enhancing yield and reducing bond failures.
40 December/January 2023
www.electronicsworld.co.uk Plasma cleaning can be applied
as an in-line solution, e.g., prior to encapsulation, or as a batch processing step, with bespoke frame loading arrangements. Batch processing involves parts being
loaded into a plasma chamber; see Figure 4. The process is quick and effective, taking no more than five minutes to complete the treatment. Alternatively, an atmospheric plasma
torch system, such as Henniker’s Cirrus unit (Figure 5), can be integrated into an in-line assembly and fully controlled by the host system to achieve localised bond- pad treatment. Plasma cleaning utilises oxygen, argon,
hydrogen, or mixtures of these gases. Various gas combinations can meet the needs of nearly every case; however, there are considerations such as the dulling of lead frames when using oxygen, or the re- deposition of metal particles in the case of argon, as well as safety concerns when using hydrogen.
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