Microarray Package Plated Pedestal Stress Displacement
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Solution Overview
Problem
Microarray packages experience increased stress and contact failure at outermost contact interfaces due to geometry and position, leading to prevalent contact failures during operational board-level thermo-cycling.
Innovation Solution
The integration of plated pedestal members that protrude beyond the bottom surface of the microarray package, axially displacing stress concentration points from the conventional solder bump plane to a different plane, enhancing the shear strength and mounting integrity by allowing solder balls to flow over and around the pedestals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of contact posts is increased to accommodate higher capacity, then the pin count and electrical interconnect capacity are improved, but the outermost contact posts are positioned further from the center causing increased shear stress and contact failure
Solution Approach 1:
The patent introduces a vertical dimension by adding pedestal members that protrude from the bottom surface of the package. This transforms the contact interface from a two-dimensional planar contact to a three-dimensional structure, allowing stress to be distributed along the height of the pedestal members rather than concentrated at the outermost contact posts.
Solution Approach 2:
The pedestal members are pre-formed and attached to contact pads before the packaging process. This preliminary structural reinforcement is built into the design, so that when the package is subjected to thermal cycling and mechanical stress, the stress concentration points are already displaced to more favorable locations within the pedestal structure.
2Ease of manufacture
If conventional solder bump mounting is used, then the manufacturing process is simple, but stress concentration occurs at the solder bump and solder plating interface plane causing contact failure
Solution Approach 1:
The pedestal members act as intermediary structures between the contact pads and the solder bumps. These pedestals provide an intermediate mounting surface that extends vertically, allowing solder balls to flow over and around them. This intermediary structure distributes the mechanical stress along the pedestal height rather than concentrating it at the solder interface plane.
Solution Approach 2:
The patent changes the geometric parameters of the contact structure by adding vertical height through pedestal members. This transforms the contact interface from a flat plane to a three-dimensional structure with extended height, thereby changing the stress distribution characteristics and displacing stress concentration points to more favorable locations.
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
Significantly improves ball shear values and board-level temperature cycling reliability by increasing the mounting integrity and lateral support, with average ball shear results increasing by about 50 grams per contact, and is cost-effective when applied to the entire array of contact posts.
Implementation Method 1
Each pedestal is plated to a height that is sufficient such that a respective stress concentration point that was formerly contained in the plane of the solder bump and solder plating interface is now axially displaced to a different plane that now extends through the pedestal
Implementation Method 2
the solder balls which flows over and around the distal surface of the pedestal members cooperate with the sidewalls of the pedestal members to strengthen mounting to the microarray package
Data Source
AI summary
A microarray package includes a leadframe having an array of contact posts, a die carried by the lead frame, and a plurality of bonding wires that electrically connect the die to the lead frame. An encapsulant is included that encapsulates the die, the bonding wire and the leadframe while leaving the distal ends of the contact posts exposed and substantially co-planar with a bottom surface of the microarray package. A plurality of pedestal members is plated to the distal end of a respective contact pad. A distal surface of each pedestal member protrudes outwardly beyond the bottom surface of the microarray package in the range of about 15 μm to about 35 μm.