Lead Frame Die Pad Constriction for Resin Adherence
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Solution Overview
Problem
Lead frames with a bilayer structure face the risk of die pads separating from the resin due to inadequate adherence, especially under stress-induced deformation, as the contact area between the die pad and resin is limited, leading to potential warping and separation.
Innovation Solution
The lead frame design incorporates a die pad with a buried portion and a rising portion, where the side surfaces of the buried portion feature a constriction that increases adherence to the resin, and the terminal also has a similar constriction to enhance bonding, using anisotropic etching and plating layers to secure the structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the die pad is buried in the resin with only side surfaces contacting the resin, then the structure is simple and easy to manufacture, but the adherence between the die pad and resin is insufficient leading to separation risk
Solution Approach 1:
The die pad is designed with different surface characteristics: the side surfaces have a smooth finish for easy manufacturing, while the bottom surface has a roughened finish to enhance resin adherence. This local differentiation of surface quality allows the structure to be easy to manufacture while simultaneously improving reliability through enhanced bonding at the critical interface.
2Device complexity
If the die pad has a simple flat structure, then the manufacturing process is simple, but the contact area with resin is small causing separation under stress
Solution Approach 1:
The bottom surface of the die pad is designed with a curved or domed shape rather than a flat surface. This curvature increases the contact area between the die pad and the resin, improving adherence and reducing separation risk under stress, while adding minimal complexity to the overall structure.
3Volume of moving object
If the die pad is fully embedded in the resin, then the structure is compact, but the contact area is limited to side surfaces only reducing adherence
Solution Approach 1:
The die pad design extends the resin contact area from only the side surfaces (one-dimensional contact) to include the bottom surface as well (two-dimensional contact). This dimensional expansion of the contact interface significantly increases the total adherence area while maintaining the compact embedded structure.
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 design significantly reduces the likelihood of die pad separation from the resin by increasing the adherence through the anchor effect of the constriction, thereby enhancing the structural integrity and reliability of the lead frame.
Implementation Method 1
the side surface is covered with the resin and has a constriction that is depressed in a direction parallel to the mount surface
Data Source
AI summary
A lead frame includes a first frame member including a die pad; a second frame member that is layered on the first frame member and that includes a lead; and a resin with which a space around the die pad and the lead is filled, wherein the die pad includes a rising portion and a buried portion, the rising portion rises from the resin, the buried portion is buried in the resin and has a mount surface on which a semiconductor element is to be mounted and a side surface that is continuous to the mount surface, and the side surface is covered with the resin and has a constriction that is depressed in a direction parallel to the mount surface.