Semiconductor Pin Intermetallic Bonding to Prevent Reflow Voiding
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Solution Overview
Problem
Semiconductor packages face challenges in maintaining structural integrity and electrical connectivity due to issues with melting temperatures and the formation of intermetallic layers during reflow processes, particularly when exposed to high temperatures, which can lead to voiding and reduced shear strength.
Innovation Solution
The implementation of semiconductor packages with a pin structure that includes a titanium sublayer, a nickel sublayer, and an intermetallic layer of either silver-tin or copper-tin, where the intermetallic layer is formed by reflowing a tin layer with a silver or copper layer, resulting in a melting temperature greater than 260 degrees Celsius, thereby preventing reflow during subsequent temperature increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a tin layer is used for bonding pins to substrates, then good wetting and adhesion are achieved, but the melting temperature is too low (231°C) causing reflow during standard reflow processes (260°C)
Solution Approach 1:
The patent applies composite materials by creating an intermetallic layer composed of multiple metals (tin, silver, copper, nickel) rather than using pure tin. This composite intermetallic structure combines the adhesion benefits of tin with higher melting point metals, achieving both strong bonding and resistance to reflow at standard temperatures.
Solution Approach 2:
The patent changes the physical and chemical parameters of the bonding material by forming intermetallic compounds through controlled reactions between tin and other metals (silver, copper, nickel). This transformation elevates the melting temperature from 231°C to above 260°C while maintaining adhesion properties through the intermetallic bonding mechanism.
2Strength
If nickel and tin are used in contact during reflow, then good adhesion is achieved, but excessive nickel-tin intermetallic formation occurs causing voiding and reduced shear strength
Solution Approach 1:
The patent introduces silver or copper as an intermediary layer between nickel and tin during the bonding process. This intermediary prevents direct excessive contact and reaction between nickel and tin, controlling intermetallic formation and preventing voiding while still achieving adequate adhesion through the controlled intermetallic layer.
Solution Approach 2:
The patent applies local quality by creating a multi-layer structure where different metal combinations are positioned strategically: tin for adhesion, silver/copper as intermediaries to control reaction, and nickel for structural support. Each layer performs its specific function locally, preventing excessive nickel-tin intermetallic formation while maintaining overall bond strength.
3Ease of manufacture
If standard reflow processes (260°C) are used for bonding, then good wetting is achieved with tin, but the tin layer reflows and causes structural defects
Solution Approach 1:
The patent performs preliminary action by pre-forming the intermetallic layer structure before the final reflow process. The multi-metal composition is prepared in advance with controlled thicknesses and arrangements, so that during standard reflow the structure remains stable and prevents tin reflo w while still achieving wetting through the controlled intermetallic formation.
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
This solution enhances the structural integrity and electrical connectivity of semiconductor packages by ensuring the intermetallic layer does not reflow during standard reflow profiles, maintaining a strong die attach and reducing the formation of nickel-tin intermetallics, which can compromise adhesion and shear strength.
Implementation Method 1
the one of the silver and tin intermetallic layer or the copper and tin intermetallic layer may be formed by reflowing a tin layer and one of a silver layer or copper layer
Data Source
AI summary
Implementations of a semiconductor package may include a pin coupled to a substrate. The pin may include a titanium sublayer, a nickel sublayer, and one of a silver and tin intermetallic layer or a copper and tin intermetallic layer, the one of the silver and tin intermetallic layer or the copper and tin intermetallic layer having a melting temperature greater than 260 degrees Celsius. The one of the silver and tin intermetallic layer or the copper and tin intermetallic layer may be formed by reflowing a tin layer and one of a silver layer or copper layer with a silver layer of the substrate where the substrate may be directly coupled to the one of the silver and tin intermetallic layer or the copper and tin intermetallic layer. The substrate may include a copper layer that was directly coupled with the silver layer before the reflow.