Diode Coupling Test Pads to Contact Pads in Semiconductor Packages
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Solution Overview
Problem
The removal of test pads from semiconductor packages is tedious, imprecise, and costly, and their presence can induce unwanted interference, limiting their use in high-speed applications due to suboptimal placement and the need for physical severance of connections after testing.
Innovation Solution
A diode with a P-N junction is used to couple the test pad to the contact pad, allowing current flow in only one direction, enabling functional disablement of the test pad without physical removal and allowing for placement at any distance without degrading signal integrity, thus eliminating the need for physical severance and optimizing high-speed testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If test pads are physically removed after testing, then interference is eliminated, but manufacturing cost and complexity increase
Solution Approach 1:
The harmful function of the test pad (acting as an antenna) is extracted by using a diode to electrically isolate it from the contact pad after testing, eliminating the need for physical removal while preventing signal interference
Solution Approach 2:
The test pad is functionally discarded after testing through diode isolation, allowing it to remain physically present on the substrate without affecting package operation, thus avoiding costly removal processes
2Measurement precision
If test pads are placed close to contact pads, then testing accuracy improves, but placement difficulty increases with high IO density
Solution Approach 1:
A diode is introduced as an intermediary component between the test pad and contact pad, allowing the test pad to be positioned optimally for testing while maintaining electrical isolation during normal operation, thus resolving the conflict between testing accuracy and placement feasibility
3Reliability
If test pads are left coupled to devices, then testing can be performed, but unwanted interference is induced during operation
Solution Approach 1:
The electrical connection between test pad and contact pad is made dynamic through a diode, allowing current flow during testing but blocking it during normal operation, thus enabling testing capability while preventing unwanted interference
4Object-affected harmful factors
If physical severance of test pad connections is performed, then interference is prevented, but manufacturing cost and time increase
Solution Approach 1:
The mechanical process of physically severing test pad connections is replaced with an electrical isolation mechanism using a diode, eliminating the need for additional manufacturing steps while still preventing signal interference
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 reduces manufacturing costs, improves the reliability and yield of semiconductor packages by enabling efficient testing of high-speed applications without signal interference and the need for physical removal of test pads, enhancing the dependability of semiconductor packages.
Implementation Method 1
A diode with a P-N junction is used to couple the test pad to the contact pad, allowing current flow in only one direction
Data Source
AI summary
Embodiments described herein provide techniques for testing a semiconductor package by using a diode to couple a test pad to a contact pad. In one scenario, a package comprises a die stack comprising one or more dies and a molding compound encapsulating the die stack. In this package, a substrate is over the molding compound. Also, a test pad and a contact pad are on a surface of the substrate. The contact pad is coupled to the die stack. A diode couples the test pad to the contact pad. In one example, the test pad is coupled to a P side of the diode's P-N junction and the contact pad is coupled to an N side of the diode's P-N junction. In operation, current can flow from the test pad through the contact pad (and the die stack), but current cannot flow from the contact pad through the test pad.