Leadframe Through-Holes Preventing Semiconductor Package Delamination
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Solution Overview
Problem
Existing methods to prevent delamination and cracking in plastic packaged semiconductor devices are only partially effective, as they fail to adequately counteract the expansive internal pressures caused by vaporized water, leading to package failure during thermal processes.
Innovation Solution
The use of a leadframe with a large assembly pad featuring through-holes and through-windows, along with additional features like ditches, grooves, and indents, which allow the packaging compound to interlock and clamp the leadframe securely, exploiting the volumetric shrinkage of the compound to counteract the expanding pressure of vaporized water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional adhesion enhancement methods (chemical purification, plasma activation, metal oxidation, coining) are used, then adhesion between device components is improved, but the adhesion strength is insufficient to counteract expansive water vapor pressure during thermal processes
Solution Approach 1:
The invention segments the assembly pad into multiple regions by forming through-holes and through-windows through it. This segmentation allows the packaging compound to penetrate and form interlocking mechanical anchors, transforming the pad from a flat adhesive surface into a three-dimensional interlocked structure that resists delamination forces more effectively.
Solution Approach 2:
The invention transitions from two-dimensional adhesion (flat pad surface bonding to compound) to three-dimensional mechanical interlocking (compound penetrating through-holes and through-windows to anchor on both top and bottom surfaces of the pad). This dimensional change creates much stronger mechanical bonds that can counteract expansive water vapor pressure during thermal processes.
2Strength
If the packaging compound is made to interlock with the leadframe through through-holes and through-windows, then clamping force is improved, but the complexity of leadframe manufacturing increases
Solution Approach 1:
The invention segments the assembly pad into multiple regions by forming through-holes and through-windows through it. This segmentation allows the packaging compound to penetrate and form interlocking mechanical anchors, transforming the pad from a flat adhesive surface into a three-dimensional interlocked structure that resists delamination forces more effectively.
Solution Approach 2:
The invention creates a porous structure in the leadframe pad by forming through-holes and through-windows. This porous configuration allows the packaging compound to penetrate and anchor mechanically, creating strong interlocking bonds. The porosity is strategically designed to provide clamping force while maintaining structural integrity.
3Strength
If additional metal layers are deposited on the leadframe, then adhesion to packaging compound is improved, but the available surface area for adhesion is reduced
Solution Approach 1:
The invention applies additional metal layers only in localized areas where wire stitch bonds need to be attached, rather than covering the entire leadframe surface. This partial application minimizes the reduction of adhesive surface area while still providing the necessary bonding functionality for wire attachments.
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 provides a stronger clamping force than the expanding water vapor, effectively preventing delamination and cracking of the package, even during thermal stress, by securely anchoring the leadframe within the packaging material.
Implementation Method 1
The polymerization process, or molecular cross linking, of thermoset compounds causes a volumetric shrinking of the polymeric material. As a consequence, the polymerized material exerts an inward-directed pressure on bodies enclosed by the thermoset compounds.
Implementation Method 2
The polymerization process, or molecular cross linking, of thermoset compounds causes a volumetric shrinking of the polymeric material.
Implementation Method 3
plastic packages made, for instance, by epoxy-based molding compounds can be penetrated by discrete water molecules within a time period of about one day
Implementation Method 4
quick rises of temperature may vaporize the water and initiate expansive internal pressures between the components and the package material
Data Source
AI summary
A semiconductor device has a leadframe with a first (401a) and a parallel second surface, and an assembly pad (410) bordered by two opposing sides, which include a plurality of through-holes (420) from the first to the second pad surface. Another pad side includes one or more elongated windows (421) between the pad surfaces. The second pad surface includes a plurality of grooves. The leadframe further has a plurality of leads (430) with opposite elongated sides castellated by indents (431). Layers (440) of bondable metals are restricted to localized areas surrounding bond spots. A semiconductor chip (450) is attached to the pad and wire-bonded (460) to the bond spots. A package (470) encapsulates the chip, wires, pad, and lead portions, and secures the leadframe into the package by filling the through-holes, windows, grooves, and indents.