Leadframe Trenches for Die Attach Control and Adhesion
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Solution Overview
Problem
Current leadless packaging techniques face issues with die attach material spreading, leading to chip tilting, cracking, alignment problems, and delamination due to inadequate adhesion of encapsulating materials, which limits the use of larger chips and efficient space utilization.
Innovation Solution
A support substrate with a flag and a bonding surface featuring a continuous trench with curved sidewalls surrounding at least 50% of the chip's peripheral edge, controlling die attach material flow and providing a surface tension effect to prevent spreading, ensuring proper chip alignment and adhesion of encapsulating materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional wire bonding and leadframe processes are used for leadless packaging, then cost structure is attractive, but die attach material spreads causing chip tilting and cracking
Solution Approach 1:
The bonding surface is segmented into multiple regions by forming trenches that divide the surface into separate bonding areas. This segmentation prevents die attach material from spreading across the entire surface, thereby maintaining chip alignment precision while preserving the cost-effective leadframe process
Solution Approach 2:
The bonding surface is modified locally by creating trenches in specific regions where die attach material spreading occurs. This local modification changes the surface properties to control material flow, preventing chip tilting and cracking without affecting the overall manufacturing process
2Strength
If die attach material is used to attach chip to leadframe, then chip is securely attached, but material spreads reducing bonding surface area for encapsulant adhesion
Solution Approach 1:
The bonding surface is divided into distinct functional zones using trenches: one zone for die attach material bonding and another zone for encapsulant adhesion. This ensures sufficient bonding strength while preserving adequate surface area for encapsulant attachment
Solution Approach 2:
The trenches extract or remove portions of the bonding surface that would otherwise be covered by spreading die attach material. This creates dedicated areas where encapsulant can adhere effectively, separating the bonding functions spatially
3Reliability
If encapsulating materials are applied to cover chip, then chip is protected, but materials do not adhere well to die attach materials causing delamination
Solution Approach 1:
Trenches are formed to expose the leadframe substrate in regions where encapsulating materials need to adhere. This extracts the problematic die attach material from the bonding surface, providing a suitable surface for encapsulant adhesion and preventing delamination
Solution Approach 2:
The trenches act as intermediary structures that facilitate better adhesion between the encapsulating material and the leadframe. By providing a dedicated bonding surface, the trenches serve as a mediator that improves the interface between different materials
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 solution reduces die attach material spread, minimizes chip tilting and cracking, enhances encapsulant adhesion, and allows for larger chips and closer chip placement, improving overall device performance and reliability by providing a moisture barrier and mold lock feature.
Implementation Method 1
provides a surface tension effect to prevent spreading
Data Source
AI summary
In one embodiment, an electronic device package (1) includes a leadframe (2) with a flag (3). An electronic chip (8) is attached to the flag (3) with a die attach layer (9). A trench (16) having curved sidewalls is formed in the flag (3) in proximity to the electronic chip (8) and surrounds the periphery of the chip (8). An encapsulating layer (19) covers the chip (8), portions of the flag (3), and at least a portion of the curved trench (16). The curved trench (16) reduces the spread of die attach material across the flag (3) during chip attachment, which reduces chip and package cracking problems, and improves the adhesion of encapsulating layer (19). The shape of the curved trench (16) prevents flow of die attach material into the curved trench (16), which allows the encapsulating layer (19) to adhere to the surface of the curved trench (16).