Exposed Thermal Pad IC Package for Visible Solder Fillets
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Solution Overview
Problem
Existing integrated circuit (IC) packages with exposed thermal pads face challenges in visual inspection of solder bonds to printed circuit boards, as the solder layer is typically covered and can only be inspected using expensive and inconvenient x-ray methods.
Innovation Solution
The IC package design includes a thermal pad with exposed peripheral surfaces and flanges, allowing for optical inspection of the solder bond between the IC package and the printed circuit board, enabling visual or machine vision inspection of the solder fillet formed during attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the thermal pad is completely enclosed in mold compound for protection, then the IC package has better protection and cleaner appearance, but the solder bond cannot be visually inspected and requires expensive x-ray methods
Solution Approach 1:
The patent extracts the peripheral portions of the thermal pad from the mold compound enclosure, creating exposed peripheral surfaces that allow visual inspection of solder bonds while maintaining the protective molding for the internal components. This selective exposure resolves the contradiction between protection and inspectability.
Solution Approach 2:
The thermal pad is segmented into different zones: a central portion that remains enclosed for protection and peripheral portions that are exposed for inspection. This segmentation allows simultaneous achievement of both protection and visual inspectability.
2Adaptability or versatility
If the thermal pad is completely enclosed in mold compound, then the package has better protection, but wave soldering attachment methods cannot be used
Solution Approach 1:
By extracting/exposing the peripheral surfaces of the thermal pad from the mold compound, the patent enables wave soldering processes to access and bond to the thermal pad edges, thereby adding manufacturing versatility while maintaining overall package protection.
3Measurement precision
If the solder layer is covered by mold compound, then the package structure is simpler and more protected, but visual or machine vision inspection of solder fillet is not possible
Solution Approach 1:
The patent extracts the peripheral regions of the thermal pad from the mold compound to create exposed surfaces. This allows optical and machine vision systems to directly observe the solder fillet formation and quality at the thermal pad periphery, enabling precise non-contact inspection.
Solution Approach 2:
The patent creates a dimensional transition by exposing the vertical sidewalls of the thermal pad through the mold compound. This exposes previously hidden lateral surfaces, providing new inspection dimensions for observing solder bond quality without compromising overall package integrity.
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 facilitates cost-effective and convenient visual inspection of solder bonds, improving the manufacturing process and enabling wave soldering attachment methods that were previously not possible with conventional packages.
Implementation Method 1
Heat from the die is conducted through the thermal pad and into the PC board where it dissipates
Implementation Method 2
the solder bond bonding a thermal pad of an exposed pad IC package to a printed circuit board
Data Source
AI summary
An IC assembly including an exposed pad integrated circuit (“IC”) package having a thermal pad with a top surface and a bottom surface and with at least one peripheral surface portion extending transversely of and continuous with the bottom surface. The bottom surface and the at least one peripheral surface are exposed through a layer of mold compound. Also, methods of making an exposed pad integrated circuit (“IC”) package assembly. One method includes optically inspecting a solder bond bonding a thermal pad of an exposed pad IC package to a printed circuit board. Another method includes wave soldering an exposed pad of an IC package to a printed circuit board.