High Bandwidth Memory (HBM) has become a crucial component of this equation. However, the HBM roadmap is no longer just about adding more bandwidth. New architectures are bringing memory and logic closer together through advanced logic-based dies, custom PHYs, memory controllers optimized for specific workloads, and increasingly application-specific functions.
For semiconductor test engineers, these changes present a range of new challenges. Higher I/O density, taller stacks, faster interfaces, higher power requirements, and more complex logic must all be reliably tested at the wafer level under increasingly demanding conditions.
In FormFactor’s upcoming webinar, “Enabling GenAI Through Advanced MEMS Probe Card: Scaling HBM and Custom HBM Test for High-Temperature, Fine-Pitch, and μBump-Array Pad Applications,” our experts will examine what these changes mean for HBM testing and the probe card technologies required to keep pace with these developments.
HBM Is Scaling Faster Than Ever
HBM has already helped address one of the fundamental challenges in AI computing: supplying data to increasingly powerful processors. But HBM is rapidly evolving into more than just a means of delivering data to increasingly powerful processors.
Industry roadmaps point to a continuous evolution from HBM3E to HBM5, accompanied by significant increases in stack height, I/O density, bandwidth, and logic integration. The number of I/Os is expected to rise from approximately 1,024 to 4,096, while future chips will transition to 16-Hi and possibly 20-Hi stacks.
At the same time, the architecture itself is changing. Earlier HBM implementations used base chips manufactured using a DRAM process, as well as standard DDR PHYs. New HBM and custom HBM designs utilize custom PHYs, controllers optimized for specific workloads, and more advanced logic within the base chip. This gives semiconductor companies more freedom to optimize memory architectures for specific workloads, including AI training and inference.
Memory, logic, and computing power are becoming increasingly integrated, offering developers more opportunities to optimize HBM for specific AI workloads. This can bring significant benefits at the system level, but it also changes the requirements for the testing process.
Why HBM Testing Is Becoming Increasingly Challenging
As HBM stacks become taller, hotter, faster, and more densely interconnected, adding more probes is only part of the testing challenge.
Thermal behavior is one example. As more chips are added to the stack, thermal resistance can increase, leading to higher operating temperatures in the core and base chips. The test hardware must still ensure reliable electrical contact even when the device and the test environment are subjected to significant thermal changes.
For the test board, this means maintaining flatness, stable contact resistance, and consistent wiping performance across the entire test area. These requirements become more difficult as temperatures rise and different materials expand at different rates.
Higher interface speeds further complicate the testing challenge. Custom PHY architectures are being developed to boost performance while making more efficient use of chip area. As interface speeds increase, test boards must support the high-frequency performance required to validate increasingly advanced HBM and custom HBM interfaces. High-frequency signal integrity is becoming an increasingly important requirement as interface speeds continue to rise.
Physical complexity is also increasing. More logic in the base chip, increasingly sophisticated controllers, finer pitch, and dense μBump array pad structures can drastically increase the number of electrical connections required during testing.
Requirements for next-generation HBM test boards may include:
- High-speed testing at frequencies above 5 GHz
- Chuck temperatures above 125 °C
- Increasing current-carrying capacity requirements
- Reliable contact across dense padarrays with fine pitch
- More than 80,000 probes per device under test (DUT)
The real challenge lies in meeting all these requirements simultaneously without compromising measurement accuracy or repeatability.
The test board must evolve alongside HBM
With advanced HBM technology, it is no longer sufficient to merely establish a reliable electrical contact. The test card must exhibit consistent mechanical behavior across a large and densely populated test area while compensating for thermal expansion. It must ensure stable electrical performance as frequencies and current requirements increase. In addition, it must repeatedly make contact with increasingly complex pad structures while ensuring contact uniformity, stable contact resistance, and precise alignment across dense test areas.
Thus, the performance of the test card is at the heart of HBM’s test strategy.
Advanced MEMS architectures offer several advantages for these applications, as they can combine high probe density with strictly controlled mechanical and electrical properties. FormFactor technologies such as SmartMatrix™ and vertical MEMS test cards are designed to meet the thermal, electrical, mechanical, and density-related requirements associated with testing advanced HBM and custom HBM.
The need for this flexibility grows as more logic is integrated into HBM architectures. Testing requirements are beginning to transcend the traditional boundaries between memory and logic testing, necessitating test board technologies capable of supporting a broader range of device architectures and operating conditions.
Upcoming Webinar: Enabling GenAI Through Advanced MEMS Test Board Technology
FormFactor’s upcoming webinar, titled “Enabling GenAI Through Advanced MEMS Test Board Technology: Scaling HBM and Custom HBM Testing for High-Temperature, Fine-Pitch, and μBump Array Pad Applications takes an in-depth look at these challenges and the technologies being developed to address them.
Attendees will learn more about:
- Computing and memory trends driving next-generation HBM and Custom HBM
- How increasing stack heights affect thermal behavior and test requirements
- High-speed HBM testing at frequencies above 5 GHz
- Testing at chuck temperatures above 125 °C
- Managing signal integrity, contact resistance stability, probe planarity, and thermal expansion
- Establishing reliable contacts across dense μBump array pad structures
- Probe architectures supporting more than 80,000 probes per device under test (DUT)
- How advanced MEMS probe card technology can meet new HBM test requirements
This webinar is the first part of a new series exploring how semiconductor test technologies help enable the silicon innovations behind the GenAI era.
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Related Links
👉 www.formfactor.com
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