MEMS EMI Shield Cap Using Conductive Adhesive and Paint
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Solution Overview
Problem
Existing electromagnetic interference (EMI) shield caps for microelectromechanical systems (MEMS) devices face adhesive failure due to contamination and inadequate surface finishing, leading to poor bonding between the adhesive layer and copper foil, which results in ineffective shielding.
Innovation Solution
The EMI shield cap design features a first and second layer of polymeric material with an aperture forming a cavity, joined by an adhesive layer and covered with electrically continuous conductive paint, where increased pressure during lamination ensures proper bonding and the adhesive forms a bead around the back wall, enhancing the adhesion and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper plating is used to line the cavity and bond BT layers, then electrical continuity and EMI shielding are achieved, but manufacturing complexity and cost increase due to multiple plating layers and surface preparation requirements
Solution Approach 1:
The patent extracts and removes the complex copper plating process entirely, replacing it with a simple conductive adhesive application. The copper plating layers (copper, nickel, gold) and associated electroplating equipment, process control, and surface preparation steps are completely taken out of the manufacturing system, achieving EMI shielding through the conductive adhesive alone.
Solution Approach 2:
The patent replaces expensive, multi-layer copper plating with a inexpensive conductive adhesive that can be applied directly to the BT layer surfaces. This disposable-like approach uses a simple, single-layer conductive material instead of expensive, multi-layer metal plating, significantly reducing material and processing costs while maintaining EMI shielding functionality.
2Reliability
If copper plating is applied to ensure electrical continuity, then EMI shielding is effective, but manufacturing time and productivity are reduced due to sequential electroplating of multiple layers
Solution Approach 1:
The conductive adhesive is applied to the BT layer surfaces before the layers are assembled and before any EMI shielding effectiveness is tested. This preliminary application of the conductive material ensures electrical continuity is established from the outset, eliminating the need for subsequent plating operations and allowing parallel processing of multiple components.
Solution Approach 2:
The patent replaces the electrochemical plating system (requiring electrolyte baths, power supplies, and complex process control) with a simple mechanical adhesive application process. The conductive adhesive is applied using conventional coating or dispensing methods, substituting complex electrochemical machinery with simple mechanical application equipment, thereby dramatically reducing manufacturing cycle time.
3Strength
If adhesive layer is made thin to allow copper plating to bridge gaps, then bonding strength is maintained, but risk of plating discontinuity increases leading to EMI shielding failure
Solution Approach 1:
The conductive adhesive serves as an intermediary material that simultaneously provides both bonding and EMI shielding functions. Instead of relying on thin copper plating to bridge gaps between BT layers, the conductive adhesive acts as the primary bonding agent and EMI shield, eliminating the gap-bridging requirement and ensuring continuous electrical coverage without the risks associated with thin plating.
Solution Approach 2:
The patent merges the adhesive bonding function and the EMI shielding function into a single material - the conductive adhesive. Rather than using separate adhesive and copper plating layers, the conductive adhesive combines both functions, ensuring that the same material provides both mechanical bonding and continuous electrical coverage for EMI shielding, thereby eliminating the reliability risk of plating discontinuity.
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
This design effectively prevents delamination and ensures adequate electromagnetic shielding, meeting mechanical strength and thermal cycle standards without the need for copper plating, while maintaining feature preservation and conductivity.
Implementation Method 1
an electrically continuous layer of conductive paint covers the back and side walls of the cavity and exposed portions of the adhesive
Implementation Method 2
The first and second layers are joined by an adhesive positioned between the layers
Data Source
AI summary
A cap for a microelectromechanical system device includes a first layer of, e.g., Bismaleimide Triazine (BT) resin material in which a through-aperture is formed, laminated to a second layer of BT resin material that closes the aperture in the first layer, forming a cavity. The first and second layers are laminated with a thermosetting adhesive that is sufficiently thick to encapsulate particles that may remain from a routing operation for forming the apertures. The interior of the cavity, including exposed portions of the adhesive, and the exposed face of the first layer are coated with an electrically conductive paint. The cap is adhered to a substrate over the MEMS device using an electrically conductive adhesive, which couples the conductive paint layer to a ground plane of the substrate. The layer of conductive paint serves as a shield to prevent or reduce electromagnetic interference acting on the MEMS device.