IO Buffer Ring Oscillator for SiP Die-to-Die Interconnection Testing
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Solution Overview
Problem
Testing die-to-die interconnections in System in Package (SiP) or 3D ICs is challenging due to encapsulation, which prevents direct probing by automatic test equipment (ATE), and existing boundary scan methods are costly and difficult to implement, especially since they require specific circuit support and test patterns.
Innovation Solution
An IO buffer with an input and output port forms a ring oscillator with an inverter feedback circuit, allowing the oscillating frequency to reflect the equivalent capacitance of the die-to-die interconnection, enabling the testing of connection states without requiring direct probing, and an optional auxiliary circuit can further analyze the frequency for determining connection states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boundary scan methodology is used to test die to die interconnection, then logic functionality can be tested, but it requires all dice to be equipped with boundary scan circuits and proper test patterns which are costly and difficult to generate
Solution Approach 1:
The invention extracts the testing functionality from the traditional boundary scan approach and implements it within a single die using an IO buffer and auxiliary circuit. This eliminates the requirement for boundary scan circuits on all dice, reducing device complexity while maintaining testing capability. The testing function is taken out of the inter-die communication requirement and localized to one die.
Solution Approach 2:
The IO buffer is designed to serve dual purposes: normal I/O operation and interconnection testing. By configuring the IO buffer to operate in different modes (normal mode and test mode), the same hardware structure achieves multiple functions, eliminating the need for separate boundary scan circuits on each die and reducing overall system complexity.
2Reliability
If boundary scan methodology is used to test die to die interconnection, then logic functionality can be tested, but proper test patterns are difficult and costly to generate or obtain
Solution Approach 1:
The testing system is self-sufficient, generating its own test patterns internally through the auxiliary circuit without requiring external test pattern generation equipment. The ring oscillator automatically produces the necessary test signals, eliminating the need for costly external test pattern generation and making the system easier to manufacture and deploy.
3Measurement precision
If direct probing by ATE is used to test interconnection, then connection state can be directly measured, but the encapsulated die to die interconnections prevent direct access
Solution Approach 1:
The invention introduces an intermediary testing mechanism using an IO buffer and auxiliary circuit that indirectly measures the connection state of die to die interconnections. Instead of directly probing the encapsulated interconnections, the system uses the oscillating frequency of a ring oscillator as an intermediary indicator that reflects the capacitance and thus the connection state, making measurement possible without direct physical access.
4Reliability
If ring oscillator testing is implemented, then die to die interconnection state can be tested through oscillating frequency, but the feedback circuit must be disconnected when testing is complete
Solution Approach 1:
The IO buffer is designed with dynamic reconfigurability, allowing it to switch between different operational modes (normal I/O mode and test mode) based on system requirements. This dynamic switching capability enables the same hardware to serve different functions without permanent structural changes, managing the complexity through controlled adaptability rather than fixed architecture.
Data Source
AI summary
Method and apparatus of testing die to die interconnection for system in package (SiP). For testing a die to die interconnection connected between two pads of two dice, an IO buffer, e.g., a bi-directional IO buffer, in one of the two dice coupled to one of the two pads is arranged. An oscillating feedback is formed between an output port and an input port of the IO buffer, such that a state, e.g., an open state, a short state or a normal state of the die to die interconnection is tested according to a timing characteristic, e.g., a frequency, of a signal of the IO buffer.