CPU vs GPU: Why AI Requires a Different Processor Architecture

By Scott Cain, Advanced Packaging Cleaning Segment Specialist, KYZEN

Traditional CPUs were designed for low-latency, sequential processing. Typically, they contain a relatively small number of powerful cores optimized for executing complex instructions in sequence. CPUs excel at general-purpose computing tasks but struggle with the highly repetitive calculations required for AI training and inference.

GPUs, by contrast, are designed for massive parallel processing. Modern AI GPUs from companies such as NVIDIA and AMD contain thousands of smaller processing cores capable of handling large numbers of simultaneous calculations. This architecture makes GPUs highly effective for AI workloads.

One of the primary reasons GPUs outperform CPUs in AI applications is the mathematical nature of machine learning algorithms. Neural networks rely heavily on matrix multiplication operations involving enormous datasets. These calculations can be broken into thousands of smaller tasks that GPUs process simultaneously.

Memory bandwidth is another critical factor. Traditional CPUs rely on DDR memory, which typically delivers bandwidth in the range of 50-100 GB/s. AI accelerators require significantly more bandwidth to move massive datasets between memory and processors. GPUs address this challenge by using High Bandwidth Memory (HBM), which can exceed 3 TB/s.

Additionally, modern GPUs now incorporate specialized processing units such as Tensor Cores and Matrix Cores, specifically designed for AI operations. These units perform matrix calculations faster and more efficiently than general-purpose CPU architecture.

Why 2.5D and 3D IC Packaging Are Necessary

As AI processors continue to scale, conventional packaging approaches face several limitations.

Breaking the Memory Wall

Traditional systems place memory devices far from the processor on the motherboard. This creates long electrical pathways that increase latency and power consumption.

In 2.5D packaging, the GPU and HBM are placed side-by-side on a silicon interposer. This dramatically reduces signal travel distance and enables thousands of high-density interconnections through micro-bumps. The result is significantly improved bandwidth, reduced latency, and improved energy efficiency.

Overcoming Reticle Size Limitations

Semiconductor manufacturing is constrained by photolithography reticle size limitations. A single silicon die can only be manufactured up to approximately 850 mm² before it exceeds reticle field limitations.

To overcome this limitation, manufacturers increasingly use chiplet architectures, where multiple smaller dies are integrated into a larger package.

2.5D packaging enables these chiplets to function as a unified system while improving manufacturing yield compared to building one large monolithic die.

Vertical Integration Through 3D IC Packaging

While 2.5D packaging places chips side-by-side, 3D IC packaging stacks chips vertically.

Technologies such as TSMC SoIC and Intel Foveros allow logic dies, memory dies, and cache components to be stacked directly on top of each other. This shortens interconnect distances from millimeters to micrometers, reducing energy consumption while increasing performance.

Reticle Size Considerations

Reticle size refers to the maximum area that lithography equipment can expose in a single manufacturing step. This limitation directly impacts advanced packaging because larger interposers often require larger cleaning areas during manufacturing. As Chip-on-Wafer-on-Substrate (CoWoS) packaging evolves to support more HMB stacks and larger GPUs, interposer size continues to increase, creating additional process complexity.

Types of CoWoS Packaging

TSMC currently offers several variations of CoWoS packaging:

• CoWoS-S uses a full silicon interposer

• CoWoS-R uses redistribution layer (RDL) technology

• CoWoS-L uses local silicon interconnect (LSI)

Each architecture offers different trade-offs in cost, performance, and manufacturability depending on application requirements.

CoWoS Manufacturing Process Flow

The CoWoS process consists of multiple complex manufacturing stages:

1. Known Good Die Preparation

GPU and HBM dies are tested before assembly to ensure only functional dies enter the packaging process. This reduces yield loss during expensive downstream assembly steps.

2. Die-to-Wafer (D2W) Stacking

During this stage:

• GPU dies are placed on the interposer wafer

• HBM stacks are added

• Thermal compression bonding (TCB) is used 

The bonding process applies heat and pressure to form solder joints. Final bond gap heights are often less than 25 microns, creating extremely narrow spaces that complicate cleaning.

Flux Cleaning 1: Chip-on-Wafer Cleaning

After die bonding, flux residues must be removed.

Single-wafer cleaning systems typically perform:

• Wash: Chemical spray cleaning while spinning the wafer.

• Rinse: Deionized water rinse.

• Dry: This may include IPA vapor drying, vacuum drying, spin drying, or heated nitrogen drying.

Central dies often require longer wash times because centrifugal cleaning forces are less effective near the wafer center.

Wafer Thinning and Through Silicon Vias (TSVs) Reveal

After cleaning:

• Wafers are thinned

• TSVs are exposed

• Electrical pathways are created for further assembly

This stage requires precise mechanical handling due to fragile wafer structures.

Bumping and Flux Cleaning 2

Copper pillar bump formation occurs next. After bumping, flux residues will remain and require an additional cleaning step. Manufacturers often use the same single-wafer cleaning equipment from the earlier cleaning step. Proper removal is critical before underfill application.

Wafer-on-Substrate (WoS) Assembly

The completed wafer assembly is mounted onto a substrate. This forms the final AI accelerator module. Due to the larger package size, this stage presents additional flux cleaning challenges.

Flux Cleaning 3: WoS Cleaning

WoS cleaning typically uses inline spray-in-air (SIA) systems. Although flux cleaning has long been standard practice, the challenges customers face continue to drive updates to process parame-ters. Each element of the cleaning process should be evaluated individually to develop the most effective overall solution.

Challenges include:

• Larger flip-chip areas

• Higher flux volume

• Increased cleaning time requirements

Manufacturers often perform multiple cleaning cycles to ensure complete residue removal.

There is growing demand for:

• More water-soluble fluxes

• Faster-dissolution cleaning chemistries

• Improved process efficiency

Underfill and Encapsulation

Underfill material is dispensed between dies to improve mechanical reliability. Molding compounds may also be added for structural protection. Any remaining contamination can compromise underfill adhesion and long-term package reliability.

Advanced Cleaning Challenges in 2.5D/3D Packaging

Cleaning advanced packages is significantly more difficult than traditional flip-chip packaging. The continual shrinking of standoffs or increasing of die size require a more focused cleaning process.

Micro-Bump Density

Micro-bumps can measure only 20-40 microns. Their extremely small spacing creates difficult-to-access cleaning regions.

Ultra-Low Standoff Heights

Package gaps are often below 15 microns. These narrow gaps trap cleaning fluids and contaminants.

Flux Entrapment

Flux residues can become trapped beneath dies. Incomplete cleaning may lead to:

• Ionic contamination

• Electrochemical migration

• Delamination

• Reliability failures

Process Throughput Challenges

Longer wash cycles reduce manufacturing throughput. Manufacturers must balance cleaning performance with production efficiency.

Cleaning Equipment Options

Two primary de-fluxing systems are commonly used:

1. Inline SIA Systems. These provide continuous movement via conveyor belt as well as higher throughput.

2. Batch Systems. Components remain stationary, resulting in greater cleaning precision.

The optimal choice depends on package design and production volume.

Chemistry Selection

As package complexity increases, chemical performance becomes increasingly important.

Cleaning chemistry selection is a critical factor in achieving overall process success. To deliver optimal performance, chemistry must exhibit several essential characteristics, beginning with a well-balanced formulation capable of effectively solubilizing flux residues while maintaining stability throughout the cleaning process. Additionally, it should be easily monitored and controlled to ensure ongoing process consistency. Equally important is evaluating how effectively chemistry can be removed during the rinse stage to prevent residual contamination. Material compatibility must also be carefully assessed to protect the integrity of all package components, particularly sensitive metals and other delicate materials.

Beyond chemistry selection, a thorough evaluation process is necessary to properly optimize operating parameters and establish process standards that drive consistent, repeatable results. Factors such as concentration, temperature, wash time, rinse parameters, and equipment settings should be optimized during testing to define a robust cleaning process that can be reliably maintained in production.

Conclusion

The rise of AI has fundamentally changed semiconductor design and packaging requirements. GPUs, HBM integration, chiplets, and advanced packaging technologies such as CoWoS are now essential for delivering the performance required by modern AI workloads.

However, these innovations introduce significant manufacturing challenges, particularly in cleaning processes. As interconnect density increases and package geometries become more complex, flux removal becomes increasingly difficult.

Successful implementation of 2.5D and 3D IC packaging requires close coordination between design engineering, process development, materials science, and cleaning chemistry providers.

As AI demand continues to grow, advanced packaging and precision cleaning will remain critical enablers of future semiconductor innovation.

Get Back to Speed with New and Improved Tech 2 Tech

Did summer break leave you feeling like you have a lot to catch up on? No worries. The new and improved version of KYZEN’s Tech2Tech (T2T) is here to help!

Tech2Tech is an educational resource that provides practical solutions to your questions about electronics, metal finishing, advanced packaging, and universal chemistry.

Our new Tech2Tech videos will be shorter and more focused. We are also investing more time in research and investigation to make all videos are both entertaining and educational. Whether you need to solve a technical challenge or simply want to expand your knowledge, these videos will offer useful information in an easy-to-watch format.

Tech2Tech videos are also great resources to share with your customers, helping them find answers and stay up to date on important industry topics.

Click here to watch the latest Tech2Tech videos from KYZEN!

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KYZEN’s Path to the Future is Clean and Clear

Technology, material substrates, and the challenges presented in cleaning them are evolving at a record pace and likely will well into the future. Thankfully, while leading in the production of effective cleaning chemistries across multiple industries, KYZEN maintains an eye to the cleaning challenges to come and continues to “Build for the Future.”

How?

By ensuring the leadership, science, and commitment to continuous improvement are in place for KYZEN to continue doing what it does best…caring for manufacturing customers around the world and providing innovative cleaning solutions for their unique needs.

The future of KYZEN’s leadership is set after the announcement in August 2026 naming R. Erik Miller as KYZEN President and Chief Operating Officer while the men who founded and built KYZEN, Kyle Doyel and Mike Bixenman remain in leadership roles for the company and its board of directors.

“KYZEN has spent nearly three decades building me, and I’ve spent that time building it alongside a team I’m proud of every day,” said Miller of his new role, “My focus hasn’t changed: deliver value to our customers, invest in our people, and build for the future. KYZEN was built to outlast me. That was always the design. My job is to make sure we keep building, with expanded facilities, deeper capabilities, leading technically, and the same commitment to doing the right thing.”

In terms of KYZEN’s sciences and continuous improvement, Director of Science Adam Klett spoke to SMT Today in September for a Q & A article about building for the future.

When asked about KYZEN’s long-term thinking and preparing manufacturers for the future, Klett said, “The future isn’t simply about cleaning better. It’s about making cleaning more predictable, more sustainable, and easier to integrate into modern manufacturing operations. At KYZEN, we’re preparing manufacturers for what’s next by investing heavily in science, application engineering, and customer collaboration to meet the growing needs of the future.”

While KYZEN continues to build for the future, with leadership in place and science ready to serve, the path to many more years of combining innovation and care is clean and clear. Click here to read more about the changes in KYZEN’s leadership and to read the full SMT Today interview with Adam Klett, click here (link when published).

 

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Send him your questions by email or click here to connect with our team of cleaning experts.