3D Conductive Ball Pad Structure for Stronger BGA Solder Joints
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Solution Overview
Problem
Current printed circuit board assembly (PCBA) interconnection structures using ball grid array (BGA) packages face issues with crack phenomena due to the poor mechanical strength of the inter-metallic compound (IMC) layer, which is prone to damage under mechanical stress.
Innovation Solution
A three-dimensional conductive ball pad structure is introduced, featuring a substrate with a pad covered by a solder mask and at least one conductive pillar protruding from the pad. The conductive pillar and a conductive ball interlock, with the conductive ball anchored to the pad, enhancing the mechanical strength of the solder joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional BGA interconnection structure with a flat pad and solder ball is used, then the manufacturing process is simple and cost-effective, but the solder joint mechanical strength is insufficient and prone to cracking under stress
Solution Approach 1:
The invention transitions from a conventional two-dimensional flat pad structure to a three-dimensional structure by adding a conductive pillar that protrudes vertically from the pad surface. This dimensional change creates a stepped configuration where the conductive ball sits on top of the pillar, increasing the solder joint's mechanical strength and resistance to cracking while maintaining manufacturing feasibility through standard PCB fabrication processes
Solution Approach 2:
The pad structure is segmented into distinct functional components: a base pad layer, a vertical conductive pillar, and a top conductive ball. This segmentation allows each component to serve its specific function - the base pad provides electrical connection to the substrate, the pillar provides mechanical reinforcement, and the ball provides the solder joint - while collectively solving the strength problem without requiring complete structural redesign
2Reliability
If the inter-metallic compound (IMC) layer is formed to enable good soldering, then electrical and mechanical interconnection is achieved, but the IMC layer becomes the weakest point and is easily damaged during mechanical stress
Solution Approach 1:
The conductive pillar acts as a pre-positioned mechanical reinforcement element that absorbs and distributes mechanical stress before it reaches the vulnerable IMC layer. By placing this stronger structural element in advance during pad fabrication, the design preemptively protects the weak IMC layer from cracking during subsequent mechanical stress events, thereby improving overall joint reliability
3Strength
If a three-dimensional conductive pillar structure is added to enhance solder joint strength, then mechanical strength increases by at least 20%, but the pad structure becomes more complex
Solution Approach 1:
The invention modifies specific geometric parameters of the pad structure - primarily the height and diameter of the conductive pillar - to achieve the optimal balance between strength enhancement and manufacturing complexity. By carefully controlling these parameters within certain ranges, the design achieves at least 20% strength improvement while keeping the structure compatible with existing PCB fabrication capabilities and assembly processes
Data Source
AI summary
A three-dimensional pad structure includes a substrate; a pad disposed on the substrate, wherein a perimeter of the pad is covered with a solder mask; and at least one conductive pillar protruding from a top surface of the pad.