Wafer Level Package Solder Balls with Elastic Core for Stress Buffering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Wafer level package integrated circuits face stress-related damage due to bending of flexible substrates during manufacturing, handling, and operation, which existing solder ball configurations are unable to effectively absorb and mitigate.
Innovation Solution
Incorporating an elastic or resilient organic-plastic core, such as Divinilbenzene cross-linked co-polymer, within solder balls, encased in a hard shell and electrical contact layer, to act as a stress buffer layer, providing mechanical strength and absorption capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder balls are used in wafer level package integrated circuits, then electrical connection to bond pads is achieved, but stress from flexible substrate bending causes permanent damage to the integrated circuit
Solution Approach 1:
The patent applies beforehand cushioning by incorporating a resilient core material (such as rubber or elastomer) at the center of the solder ball. This resilient core acts as a pre-positioned stress-absorbing element that cushions the integrated circuit against bending forces from the flexible substrate before damage occurs. The resilient material deforms under stress, absorbing mechanical energy and preventing stress transmission to the bond pad and integrated circuit structure.
Solution Approach 2:
The patent employs composite materials by creating a multi-layer solder ball structure consisting of a resilient core material surrounded by a solder shell. This composite structure combines the stress-absorbing properties of elastomeric materials with the electrical conductivity and bonding capabilities of solder materials. The composite design allows the solder ball to simultaneously provide mechanical cushioning and electrical connection functions, resolving the contradiction between reliability and stress exposure.
2Area of stationary object
If chip scale packages are used to reduce package size, then footprint is minimized, but stress concentration at solder ball attachment region increases
Solution Approach 1:
In chip scale packages where the integrated circuit size is minimized, the resilient core within the solder ball provides beforehand cushioning by absorbing stress concentrations that occur at the solder ball attachment region. The resilient material deforms under bending loads, preventing stress from concentrating at critical interfaces between the rigid integrated circuit and the flexible substrate, thereby protecting the compact package structure.
Solution Approach 2:
The patent applies parameter changes by modifying the mechanical properties of the solder ball through the inclusion of a resilient core. This changes the stress distribution parameters at the solder ball attachment region, transforming the rigid stress transmission characteristic into a more compliant stress-absorbing behavior. The resilient core alters the local mechanical parameters to reduce stress concentration while maintaining the compact chip scale package dimensions.
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 protects integrated circuits from mechanical and thermal stresses, enhancing reliability and performance, particularly in chip scale packages with high bump counts, by absorbing forces and maintaining electrical contact.
Implementation Method 1
Each elastic or resilient material core may include an organic-plastic material, such as Divinilbenzene cross-linked co-polymer of relatively high resistance. It has a relatively good elongation property so that it can effectively absorb forces exerted on the integrated circuit
Implementation Method 2
The elastic or resilient core serves as a stress buffer layer in a wafer level package (WLP) integrated circuit... the solder balls can further assist in effectively protecting the integrated circuit during manufacturing, handling, and operation
Data Source
AI summary
An integrated circuit including solder balls containing an elastic or resilient material core, a hard or rigid shell substantially enclosing the core, and an electrical contact layer substantially enclosing the shell. The elastic or resilient core serves as a stress buffer layer in a wafer level package (WLP) integrated circuit. The elastic or resilient material core may include an organic plastic material, such as a Divinilbenzene cross-linked co-polymer of relatively high resistance. This material has a relatively good elongation property so that it can effectively absorb forces exerted upon the integrated circuit by, for example, the flexing of a printed circuit board (PCB) or other structure to which the integrated circuit is attached. The hard or rigid shell serves to contain the elastic or resilient core and may include copper. The electrical contact layer serve to provide a good adhesive electrical contact to an under bump metallization (UBM) layer, may include a lead free, Tin-Gold (SnAg) material.