Conductive Epoxy Bond Pads for Flexible Substrates
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Solution Overview
Problem
Attaching surface mount devices (SMDs) to flexible substrates, such as polyethylene terephthalate (PET), is challenging due to the brittleness of cured epoxy adhesives, which can crack when the substrate is bent, leading to circuit failure, and existing conductive inks' adhesion is compromised by solvents in commercially available epoxy-based adhesives.
Innovation Solution
Applying strips of conductive epoxy as bond pads on the flexible substrate, oriented to resist cracking when bent, and using a second layer of epoxy to attach SMDs, with the dimensions and orientation of the bond pads determined by the expected bending radius and orientation, ensuring strong adhesion and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cured epoxy adhesive is used to attach SMDs to flexible substrate, then strong bonding strength is achieved, but the adhesive becomes brittle and cracks when substrate is bent
Solution Approach 1:
The bond pad is segmented into two distinct layers: a flexible adhesive layer in contact with the substrate and a rigid conductive epoxy layer on top. This segmentation allows each layer to perform its optimal function - the flexible layer prevents cracking during bending while the rigid layer provides strong bonding and electrical conductivity.
Solution Approach 2:
The invention uses a composite structure combining flexible adhesive material with rigid conductive epoxy. This composite approach allows the bond pad to simultaneously achieve flexibility (to prevent cracking) and rigidity (for strong bonding and conductivity), resolving the contradiction between strength and crack resistance.
2Strength
If commercially available epoxy-based adhesive is used, then strong adhesion is achieved, but solvents in the adhesive compromise the adhesion of conductive inks
Solution Approach 1:
The flexible adhesive layer is applied and cured first to establish strong substrate bonding. Then the conductive epoxy is applied on top of this already-cured layer, preventing solvent interaction with the conductive ink. This preliminary action sequence resolves the adhesion conflict by establishing the adhesive layer before ink deposition.
Solution Approach 2:
The flexible adhesive layer acts as an intermediary barrier between the epoxy solvent and the conductive ink. This intermediate layer prevents the solvent from compromising the ink adhesion while still allowing the epoxy to provide its bonding and conductive functions.
3Reliability
If bond pads are oriented perpendicular to bending direction, then cracking is resisted, but manufacturing complexity increases
Solution Approach 1:
The invention changes the material parameter of the bond pad, making the bottom layer flexible rather than rigid. This parameter change allows the bond pad to accommodate bending stresses in any orientation without cracking, eliminating the need for specific orientation arrangements and reducing manufacturing complexity.
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 method provides reliable attachment and electrical connectivity of SMDs to flexible substrates, maintaining circuit integrity even under bending, by using conductive epoxy strips that resist cracking and ensuring strong bonding without compromising the adhesion of conductive inks.
Implementation Method 1
Strips of conductive epoxy are applied to the flexible substrate and oriented to avoid cracking when the substrate is bent
Implementation Method 2
these epoxy strips will form conductive bond pads for attaching SMDs to the flexible substrate and will also provide the conductive contacts for a printed circuit
Data Source
AI summary
Techniques are disclosed for attaching SMDs to a flexible substrate using conductive epoxy bond pads. Each bond pad includes a set of elongated strips of conductive epoxy that are applied and cured onto the flexible substrate in an adjacent and parallel fashion. The bond pads are used to attach SMDs to the flexible substrate and also provide the conductive contacts for a printed circuit. A circuit may be printed on the flexible substrate using conductive ink that partially covers the bond pads, leaving a portion of the pads exposed. A second layer or strip of conductive epoxy may be applied over and across the exposed portions of the bond pad strips in order to attach an SMD. The number, size, and orientation of the epoxy bond pad strips may be determined by the amount of bending the flexible substrate is expected to withstand and/or the orientation of the bend.