Vacuum-Assisted EMI Shield Filling on PCB Mold Caps
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Solution Overview
Problem
Conventional techniques for forming internal EMI shields within electronic modules are time-consuming and prone to defects such as epoxy dimples, voids, and overflow, leading to increased fabrication costs and performance degradation due to internal electromagnetic interference.
Innovation Solution
The method involves forming continuous trenches in a mold cap and using a pressure differential to efficiently fill these trenches with conductive epoxy, eliminating voids and overflow by creating a vacuum that draws the epoxy through the channels, and optionally using elastomeric pads with corresponding grooves to ensure even distribution and minimize shrinkage-related defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dispensing needles are used to inject conductive epoxy into the mold cap in a piecemeal manner, then compartment EMI shields can be formed, but the fabrication process becomes time-consuming and produces defects such as epoxy dimples, voids, and overflow
Solution Approach 1:
The mold cap is segmented into multiple channels that guide the conductive epoxy to specific locations. This segmentation allows simultaneous filling of multiple EMI shield locations through a single continuous injection process, eliminating the need for piecemeal injection with multiple needles and thereby reducing fabrication time while maintaining precision through controlled epoxy flow paths
Solution Approach 2:
The mold cap is pre-configured with integrated channels and cavities during manufacturing. These pre-formed pathways ensure that when conductive epoxy is injected, it automatically flows to the correct locations in controlled amounts, preventing defects like overflow and voids without requiring complex real-time control during the injection process itself
2Reliability
If conductive epoxy is injected using dispensing needles, then EMI shields are formed, but defects such as epoxy voids and dimples occur due to incomplete injection and shrinkage during oven curing
Solution Approach 1:
The mold cap channels act as an intermediary between the epoxy injection source and the final EMI shield locations. These channels control the epoxy flow rate and distribution, ensuring complete filling of all cavities simultaneously while compensating for shrinkage during curing, thereby eliminating voids and dimples without requiring precise control of the injection needle itself
Solution Approach 2:
The epoxy injection process is transformed from discrete, piecemeal injections into a single continuous flow through the mold cap channels. This continuous action ensures that all EMI shield locations are filled simultaneously and completely, preventing the incomplete injection that leads to voids and dimples during subsequent curing
3Quantity of substance
If numerous singular injections are performed to form EMI shields, then complete coverage is achieved, but the process becomes time-consuming and costly
Solution Approach 1:
Multiple epoxy injection operations are merged into a single continuous injection process. The mold cap channels distribute the epoxy from one injection source to multiple EMI shield locations simultaneously, achieving complete coverage of all required areas in one operation rather than requiring numerous sequential injections, thereby dramatically reducing fabrication time and cost
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 approach reduces fabrication time and eliminates defects in the EMI shields, providing effective compartmental shielding that minimizes internal electromagnetic interference while maintaining the structural integrity of the electronic components.
Implementation Method 1
using a pressure differential to efficiently fill these trenches with conductive epoxy, eliminating voids and overflow by creating a vacuum that draws the epoxy through the channels
Data Source
AI summary
A method is provided for forming an internal electromagnetic interference (EMI) shield in a mold cap formed over a printed circuit board (PCB). The method includes forming a trench in the mold cap, the trench extending continuously from a first edge of the mold cap to a second edge of the mold cap, where the trench defines a trench pattern corresponding to desired locations of the internal EMI shield. The method further includes sealing an elastomeric pad on a top surface of the mold cap to form a channel, the channel including at least the trench formed in the mold cap; and filling the channel with a conductive epoxy using a vacuum configured to draw the conductive epoxy from a dispenser, connected to the first edge of the mold cap, through the channel to the second edge of the mold cap based on pressure differential.