Lead Frame Concave Edges for Mold Compound Delamination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The increased reflow temperature due to the use of lead-free solder in semiconductor devices causes mold compound delamination from the lead frame, leading to potential corrosion and damage from environmental moisture and chemicals, as existing lead frames fail to provide a strong mechanical lock with the mold compound.
Innovation Solution
The implementation of a lead frame with increased concave shapes along all exposed edges, achieved through stamping and subsequent etching, enhances the mechanical lock between the mold compound and the lead frame, with concavity depths specified as a function of lead frame thickness to accommodate thermal expansion differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free solder is used in semiconductor devices, then the solder reflow temperature increases to approximately 260 degrees Celsius, but the mold compound delaminates from the lead frame
Solution Approach 1:
The lead frame edges are formed with concave curvatures that create a mechanical interlock structure. When mold compound is applied, it flows into these concave regions and cures, creating a locked configuration that prevents delamination during thermal cycling and reflow operations.
Solution Approach 2:
The invention modifies the geometric parameters of the lead frame by introducing specific concave depths and radii along the edges. These parameter changes create a physical locking mechanism that increases the adhesion strength between the mold compound and lead frame, enabling the assembly to withstand higher reflow temperatures without delamination.
2Object-affected harmful factors
If the mold compound is applied to the lead frame, then the die and wire bonds are protected from corrosion, but the mold compound delaminates during testing and operational conditions
Solution Approach 1:
The concave curvatures on the lead frame edges create a mechanical interlock that physically locks the mold compound in place. This curved geometry prevents the mold compound from delaminating during testing and operational conditions while maintaining its protective function against corrosion and environmental moisture.
3Ease of manufacture
If conventional stamped lead frames are used, then the manufacturing process is simple, but the mechanical lock with mold compound is insufficient
Solution Approach 1:
The concave curvatures are integrated into the stamping process itself, allowing the lead frame to be formed in a single operation. The stamping die includes corresponding convex features that create the concave curvatures on the lead frame edges, maintaining manufacturing simplicity while significantly increasing mechanical lock strength.
Solution Approach 2:
The invention optimizes specific geometric parameters of the concave curvatures, including depth, radius, and spacing, to achieve the optimal balance between mechanical lock strength and manufacturing feasibility. These parameter optimizations ensure strong adhesion without compromising the simplicity of the stamping process.
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 ensures improved adhesion and protection of the semiconductor device components by maintaining the mold compound securely attached to the lead frame, preventing corrosion and damage from environmental factors.
Implementation Method 1
The deeper concavity is achieved by etching the lead frame after stamping.
Data Source
AI summary
A method includes forming a packaged integrated circuit that includes forming a lead frame by separating an outer portion of the metal structure into a plurality of leads by stamping. The plurality of leads have sides with a first concavity. The lead frame is further formed by performing an etch on the sides of the plurality of leads to achieve a second concavity on the sides of leads. The second concavity is greater than the first concavity. A semiconductor die is attached to a center portion of the metal structure. Electrical attachments are made between the die and the leads.