Exposed Thermal Pad IC Package for Optical Solder Inspection
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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
1Reliability
If the thermal pad is completely enclosed by mold compound for protection, then the IC package achieves better protection and environmental sealing, but the solder bond becomes invisible and inspection requires expensive x-ray methods
Solution Approach 1:
The patent extracts a portion of the mold compound to create an exposed region of the thermal pad's peripheral surface. This removal of material allows the solder bond to remain visible after attachment, enabling optical inspection methods while the remaining mold compound continues to provide protection and sealing for the enclosed portions of the thermal pad and internal components.
Solution Approach 2:
The thermal pad surface is segmented into different regions: an exposed peripheral surface portion that remains visible for inspection purposes, and enclosed portions covered by mold compound for protection. This segmentation allows simultaneous achievement of both inspection capability and protective enclosure.
2Ease of manufacture
If conventional fully enclosed IC packages are used, then manufacturing is simpler, but visual inspection of solder bonds is impossible and wave soldering cannot be performed
Solution Approach 1:
By removing a portion of the mold compound to expose the thermal pad's peripheral surface, the patent enables wave soldering and visual inspection capabilities while maintaining relatively simple manufacturing processes. The exposed surface allows solder to be applied and inspected optically, expanding manufacturing flexibility without significantly complicating the molding process.
3Measurement precision
If x-ray inspection is used to inspect covered solder bonds, then complete inspection coverage is achieved, but inspection cost and complexity increase significantly
Solution Approach 1:
The patent removes a portion of the mold compound to create an exposed thermal pad surface, which allows the solder bond to be inspected using simple optical methods. This eliminates the need for expensive and complex x-ray inspection equipment while maintaining adequate inspection capability for the solder joint quality.
Solution Approach 2:
The patent replaces expensive x-ray inspection with inexpensive optical inspection methods. By exposing the solder bond through the removed mold compound region, standard optical microscopes or machine vision systems can be used instead of costly x-ray equipment, significantly reducing inspection costs.
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
inspection of the solder bond bonding the thermal pad 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.