BGA Electrode Mound Metal Prevents Water and Solder Invasion
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Solution Overview
Problem
Semiconductor devices with ball grid array (BGA) packages face issues with water and solder invasion due to gaps between metal layers and passivation films, caused by poor adhesion and thermal stress, leading to potential corrosion and short circuits.
Innovation Solution
A semiconductor device design featuring a seed layer, mound metal, and interconnection where the mound metal surrounds the seed layer and acts as a barrier during electroless plating, preventing lateral extension and enhancing adhesion, thus preventing water and solder invasion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal layer is used as under bump metal (UBM) to protect interconnection from moisture and solder, then protection effectiveness is improved, but adhesion to passivation film deteriorates
Solution Approach 1:
The metal layer is segmented into two distinct parts: a mound metal portion that contacts the passivation film and provides adhesion, and an interconnection portion that provides protection. This segmentation allows each part to optimize its function - the mound metal ensures strong bonding while the interconnection maintains protective barriers.
Solution Approach 2:
Different regions of the metal structure are given different functions and properties. The mound metal portion is designed with superior adhesion characteristics to bond with the passivation film, while the interconnection portion maintains its protective function. This local differentiation resolves the contradiction by ensuring adhesion where needed without compromising protection elsewhere.
2Strength
If thermal stress treatment is applied to the semiconductor device, then interconnection strength is improved, but gap formation between metal layer and passivation film occurs
Solution Approach 1:
The mound metal structure is designed in advance to accommodate and cushion the thermal stress that will be applied during subsequent heat treatments. By creating a robust mound metal foundation before thermal processing, the structure is pre-prepared to withstand the stress without forming gaps, thus preventing reliability issues before they occur.
3Device complexity
If the interconnection is placed close to the passivation film for compact design, then device compactness is improved, but water and solder invasion risk increases
Solution Approach 1:
The seed layer acts as an intermediary barrier between the interconnection and the passivation film. It provides a protective interface that prevents direct contact between the metal interconnection and the insulating passivation film, thereby blocking the invasion path for water and solder while allowing the structure to remain compact.
Solution Approach 2:
The electrode structure uses a composite arrangement of different materials (mound metal, seed layer, interconnection metal) with complementary properties. The seed layer, being electrically insulating or having lower conductivity, provides both electrical isolation and physical barrier functions, enabling compact design without compromising protection against harmful factors.
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 solution effectively suppresses the invasion of water and solder into the semiconductor device, improving reliability by maintaining the integrity of interconnections and preventing corrosion and short circuits.
Implementation Method 1
forming an interconnection on the seed layer by electroless plating
Implementation Method 2
the mound metal forms no gap against the seed layer
Data Source
AI summary
A semiconductor device of the ball grid array (BGA) type, the device having an electrode, and a process of forming the electrode are disclosed. The electrode includes an insulating film, a seed layer on the insulating film, a mound metal on the insulating film and an interconnection on the seed layer. The mound metal surrounds the seed layer without forming any gap therebetween. The interconnection, which is formed by electroless plating, is apart from the insulating film with the mound metal as an extension barrier for the plating.