Semiconductor Board Nickel Barrier for Hermetic Sealing
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Solution Overview
Problem
Existing semiconductor package sealing technologies face issues with hermetic sealing due to changes in the melting point of brazing materials caused by alloy formation between copper-nickel alloy layers and silver-copper brazing materials under heat, leading to potential cracks and uneven joints.
Innovation Solution
A board structure comprising a substrate with an iron-nickel alloy, a copper layer, and a nickel film at the lower surface, along with a second nickel film that reduces thermal expansion mismatch and prevents copper alloy formation, ensuring a stable seal and reduced deformation under heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper-nickel alloy layer is used to prevent oxidation and improve brazing affinity, then the brazing affinity and oxidation resistance are improved, but the melting point of the brazing material changes due to alloy formation under heat, compromising hermetic sealing
Solution Approach 1:
A nickel layer is introduced as an intermediary between the copper-nickel alloy layer and the silver-copper brazing material. This nickel layer acts as a barrier that prevents direct contact and alloy formation between the copper-nickel layer and brazing material during heating, while still allowing effective heat transfer and brazing to occur. The nickel intermediary layer thus preserves the brazing affinity benefits of the copper-nickel layer without compromising the melting point stability of the brazing material.
Solution Approach 2:
The sealing structure is segmented into multiple distinct layers: substrate, oxidation-resistant layer, copper-nickel alloy layer, nickel barrier layer, and brazing material layer. This segmentation separates the functions of oxidation resistance, brazing affinity, and thermal barrier properties into different layers, preventing harmful interactions while maintaining individual layer benefits.
2Strength
If the copper-nickel alloy layer and brazing material form an alloy under heat, then the joining strength may improve, but the melting point changes and cracks may form, reducing joint reliability
Solution Approach 1:
The nickel layer serves as a thermal intermediary that allows heat to pass through while preventing chemical interaction. This maintains the thermal coupling necessary for strong brazing joints without allowing the harmful alloy formation that would change melting points and create cracks under thermal stress.
Solution Approach 2:
Different layers are assigned specific local qualities: the copper-nickel layer provides localized oxidation resistance and brazing affinity, while the nickel barrier layer provides localized prevention of unwanted alloying. This localized functional assignment allows each layer to optimize its specific role without compromising overall joint reliability.
3Device complexity
If a simple substrate structure is used, then the manufacturing complexity is reduced, but the thermal expansion mismatch causes deformation and cracking under heat, compromising seal integrity
Solution Approach 1:
The substrate structure is designed as a composite with multiple layers having different thermal expansion coefficients. The nickel barrier layer, in particular, has a thermal expansion coefficient that matches the substrate, creating a composite structure that compensates for thermal expansion mismatches and prevents deformation and cracking under thermal stress.
Solution Approach 2:
The thermal expansion parameters of the substrate system are modified by adding layers with specific thermal expansion properties. The nickel barrier layer's thermal expansion coefficient is selected to match the substrate, changing the overall thermal response of the structure to prevent warpage and maintain seal integrity under temperature variations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The board effectively maintains a tight seal and reduces deformation and cracking by minimizing thermal stress and alloy formation, ensuring reliable joining of semiconductor packages without separate bond preparation, enhancing productivity and joint stability.
Implementation Method 1
a nickel layer which prevents oxidation of the iron-nickel alloy substrate
Implementation Method 2
a copper-nickel alloy layer having a third thermal expansion coefficient equal to or close to an austenite phase of the iron-nickel alloy substrate when the austenite phase is transformed into the ferrite phase by cooling, thereby reducing thermal stress
Implementation Method 3
a nickel film at the lower surface of the copper layer... prevents copper alloy formation
Data Source
AI summary
A board in an aspect of the present invention includes a substrate, a first film, a first layer, and a second film. The substrate has a first elastic modulus. The first film is at an upper surface of the substrate. The first layer is at a lower surface of the substrate. The first layer has a second elastic modulus lower than the first elastic modulus and has a first thermal expansion coefficient. The second film is at a lower surface of the first layer. The second film includes the same material as the first film and has a second thermal expansion coefficient lower than the first thermal expansion coefficient.