Molding Small Form Factor Memory Cards Using High Melt Flow Resin
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Solution Overview
Problem
Current methods for manufacturing thin form factor digital memory cards, such as SD and MMC, are limited by the inability to apply injection molding to PCA assemblies using TSOP packages due to height constraints, and the COB process is costly and prone to defects, especially with the need for soft gold wirebonding and encapsulation steps.
Innovation Solution
A method using high melt flow index thermoset resin injection molding with strategically located runner gates to encapsulate PCA subassemblies with TSOP packages, reducing the risk of damage and allowing for a solid, integral cover that meets design specifications, while eliminating the need for soft gold wirebonding and encapsulation costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If injection molding is applied to PCA assemblies with TSOP packages, then manufacturing cost is reduced and productivity is improved, but the TSOP package height causes insufficient gap for mold material flow
Solution Approach 1:
The patent changes the physical parameters of the mold material by using high melt flow index thermoset resin. This material has superior flow characteristics that enable it to fill the narrow gap above TSOP packages during injection molding, resolving the contradiction between manufacturing efficiency and insufficient gap height
Solution Approach 2:
The patent strategically positions runner gates at specific locations (above the rows of external leads along opposite sides of the TSOP package) to control the three-dimensional flow path of the mold material. This dimensional positioning ensures proper material distribution despite the limited gap height
2Ease of manufacture
If conventional injection molding is used with TSOP packages, then cost is reduced, but the IC may be damaged by lateral shear forces and bending forces
Solution Approach 1:
The patent performs preliminary action by strategically locating runner gates above the external leads before injection begins. This positioning ensures that the mold material first covers and reinforces the leads and solder connections, preventing damage before the main injection occurs
Solution Approach 2:
The patent applies beforehand cushioning by using the initial flow of mold material from strategically positioned runner gates to reinforce the TSOP package connections. This creates a protective cushion that absorbs and distributes forces, preventing damage to the IC package during the molding process
3Reliability
If COB process with soft gold wirebonding is used, then electrical connection is achieved, but manufacturing cost increases and defect rate increases
Solution Approach 1:
The patent extracts and eliminates the soft gold wirebonding step from the manufacturing process. By using TSOP packages with direct solder connections instead of wire bonds, the patent removes the costly and defect-prone wirebonding operation while maintaining reliable electrical connections
Solution Approach 2:
The patent replaces the expensive soft gold wirebonding process with a more economical direct solder connection approach using TSOP packages. This substitution uses simpler, less expensive materials and processes while achieving the same functional result
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 enables cost-effective, high-yield production of memory cards with improved mechanical robustness, moisture resistance, and dimensional stability, applicable to both COB and TSOP assemblies, without damaging the TSOP packages or their connections.
Implementation Method 1
a high melt flow index (e.g., of at least 10) thermoset resin material is injected into a mold cavity to reliably cover and surround the PCA subassembly
Implementation Method 2
the resin material will flow into the narrow gap above the TSOP package while complying with the final finished memory card thickness requirement
Data Source
AI summary
A method for molding digital storage memory cards such as, for example, multimedia cards (MMC), secure digital cards (SD), and similar small form factor digital memory cards. A PCA subassembly including, for example, a leadframe (TSOP) package for enclosing a flash IC and a (e.g., land grad array) controller package for enclosing a controller IC are mounted on a printed wiring board within a mold cavity. A high melt flow index resin is injected into the mold cavity to form an integral, solid body within which to completely encapsulate the flash IC and controller packages and form a cover over top the flash IC package so as to maintain the required memory card height tolerance. In one embodiment, the resin material is injected downwardly into the mold cavity from locations above the respective rows of leads of the flash IC package. In another embodiment, the resin material is injected laterally into the mold body from locations at opposite sides thereof adjacent the respective rows of leads of the flash IC package.