Chip on Film Test Pad with Segmented Base Film Regions
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Solution Overview
Problem
The increasing complexity of wiring patterns in chip on film (COF) packages for flat panel displays poses challenges in efficiently testing the electrical characteristics of driving ICs, leading to potential shorts between conductive layers during the testing process.
Innovation Solution
A test pad design with a base film divided into regions of varying thickness, where the conductive layers are located in a thicker region and the probe needles are fixed in a thinner region, preventing movement and potential shorts during the testing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the base film is made thinner to reduce package size, then the size of the COF package decreases, but the probe needles may move to adjacent conductive layers causing shorts
Solution Approach 1:
The base film is segmented into regions with different thicknesses: a first region with greater thickness for supporting conductive layers and a second region with smaller thickness for probe needle contact. This segmentation allows the package to be compact overall while maintaining structural integrity where needed.
Solution Approach 2:
Different regions of the base film are given different local qualities (thicknesses) to serve different functions. The thicker first region provides mechanical support and electrical isolation, while the thinner second region enables probe needle access, optimizing both reliability and size.
2Productivity
If the spacing between conductive layers is reduced to increase wiring density, then the number of I/O connections increases, but the risk of probe needle shorts between layers increases
Solution Approach 1:
The problem of lateral spacing between conductive layers is solved by introducing a vertical dimension - varying the thickness of the base film. The thicker first region creates vertical separation that prevents probe needles from bridging adjacent conductive layers even when they are closely spaced horizontally.
Solution Approach 2:
The thicker first region of the base film acts as an intermediary barrier between adjacent conductive layers, physically preventing probe needles from making unintended contact with neighboring layers while allowing the layers to be closely spaced for high density.
3Ease of manufacture
If the base film thickness is uniform to simplify manufacturing, then the manufacturing process is easier, but probe needles cannot be properly fixed and may move during testing
Solution Approach 1:
The base film is divided into functionally distinct segments with different thicknesses. The first region (thicker) provides structural support and probe fixation, while the second region (thinner) allows probe contact, with the segmentation enabling both manufacturing feasibility and operational reliability.
Solution Approach 2:
Local variations in base film thickness are introduced to create different functional zones. The thicker areas provide the mechanical properties needed for probe fixation, while thinner areas facilitate electrical contact, allowing the structure to meet both manufacturing and testing requirements.
Data Source
AI summary
A chip on film (COF) package in which a predetermined driving integrated circuit (IC) is mounted includes a wiring structure connected to the driving IC, and a test pad connected to the wiring structure, wherein the test pad includes a base film divided into a first region and a second region, and a conductive layer located in the first region, and the second region is surrounded by the first region in a plan view.