Magnetic Underfill for Coreless Package Signal Integrity
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Solution Overview
Problem
Coreless integrated circuit packages face challenges with impedance discontinuity due to extra capacitance from ball grid array (BGA) pads, which affects signal integrity, especially at high speeds, and lack of a thick core to reduce capacitance.
Innovation Solution
Incorporating magnetic underfill, a resin mixed with ferrite powder or ferromagnetic materials, adjacent to BGA connection members and pads to increase inductance, balancing capacitance and reducing impedance discontinuity, while controlling the resin's flow during reflow using a glass temperature higher than the BGA's reflow temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic underfill is added to increase inductance, then signal integrity is improved by reducing impedance discontinuity, but device complexity increases
Solution Approach 1:
Magnetic underfill is introduced as an intermediary material positioned between the BGA connection members and the substrate. This underfill contains ferromagnetic particles that increase local inductance, serving as a mediator to compensate for capacitance effects and reduce impedance discontinuity at the connection interface.
Solution Approach 2:
The inductance parameter of the connection path is modified by incorporating magnetic materials into the underfill. By changing the magnetic permeability of the underfill material, the local inductance is increased to counterbalance the capacitance-induced impedance discontinuity, thereby improving signal integrity.
2Manufacturing precision
If resin glass temperature is increased above BGA reflow temperature to control flow, then manufacturing precision is improved, but process complexity increases
Solution Approach 1:
The glass transition temperature of the resin is selected to be higher than the BGA reflow temperature. This parameter selection ensures that the resin remains viscous and does not flow excessively during the reflow process, enabling precise positioning of the magnetic underfill without requiring additional flow control mechanisms.
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 magnetic underfill effectively increases the inductance of BGA connections, offsetting extra capacitance and improving signal integrity by reducing impedance discontinuity, making the solution applicable to both cored and coreless packages.
Implementation Method 1
The magnetic underfill may include resin mixed with magnetic materials. The resin may include epoxy and the magnetic material may include ferrite powder and/or ferromagnetic materials. The mixture may be selected based upon a desired permeability.
Implementation Method 2
The mixture may be selected based upon a desired permeability
Implementation Method 3
The resin may have a glass temperature higher than the ball grid array's reflow temperature so flow of the resin can be controlled during reflow.
Data Source
AI summary
A system to improve core package connections may include ball grid array pads, and a ball grid array. The system may also include connection members of the ball grid array conductively connected to respective ball grid array pads. The system may further include magnetic underfill positioned adjacent at least some of the connection members and respective ball grid array pads to increase respective connection members' inductance.