ATE testing challenges of heterogeneous silicon chips with advanced packaging

The semiconductor industry is rapidly evolving, driven by the increasing demand for more powerful, efficient, and versatile devices. This evolution has led to the development of complex heterogeneous semiconductor chips with ultra-high density and advanced silicon packages. These cutting-edge designs integrate various functionalities, materials, and technologies onto a single chip, making them incredibly powerful but also posing significant testing challenges in the manufacturing flow.

By Sriharsha Vinjamury, Principal Engineer, SOPT, ARM Inc

The push for heterogeneity in silicon packages is aimed at enhancing computational performance, energy efficiency, and system adaptability. By integrating various types of processors—such as CPUs, GPUs, FPGAs, and AI accelerators—these packages can optimize task execution. Heterogeneous integration enables specific processors to handle workloads they are architecturally optimized for, resulting in significant energy savings and performance boosts. Additionally, it facilitates system upgrades and customization, allowing new functionalities to be added without necessitating a complete system redesign. Enhanced thermal management techniques distribute the computational load more evenly, maintaining lower operating temperatures and improving component reliability.

This approach drives innovation, enabling bespoke solutions for applications ranging from hyperscale data centers to portable consumer electronics. Furthermore, it is cost-effective, extending the operational lifespan of technology and minimizing the frequency and cost of updates.

Silicon Performance improvements with heterogeneous Integration.

A heterogeneous package with 3D HBM memory stacking and an AI accelerator chip
Challenges faced in Advanced Packages:

One of the primary issues in advanced packaging is material compatibility and selection. Ensuring strong adhesion between diverse materials such as organic substrates, silicon dies, and metal interconnects is critical. Poor adhesion can lead to delamination, impacting device reliability. Additionally, different materials have varying coefficients of thermal expansion (CTE), which can cause mechanical stress during thermal cycling, potentially resulting in cracks or warpage.

Lithography and patterning also pose significant challenges. Achieving precise patterning for redistribution layers (RDLs) and interconnects at sub-micron scales is difficult. Variations in these processes can cause electrical performance issues and reduce yield. Accurate alignment between multiple layers in multi-die or 3D ICs is crucial, as misalignment can result in connectivity failures and diminished performance.

The nano-scale lithography for the RDL layers pose issues for reduced line widths, requiring precise electromigration control. Integrating low-k dielectrics and novel metals demands strong adhesion and diffusion barriers. Efficient thermal management and stress-relief structures are crucial for differential CTE-induced stress. Maintaining high-frequency signal integrity and controlling defects in photolithography, etching, and plating are essential for yield and reliability in complex, high-density interconnects.

A Heterogeneous Package with 3D HBM memory stacking and an AI accelerator chip.

Thin wafer handling is nothera major challenge in advanced packaging because thinning wafers to just a few hundred micrometers for 3D stacking makes them fragile and prone to breakage and warpage, necessitating special handling during processing. Through-silicon vias (TSVs) add another layer of difficulty with their complex etching and filling processes; defects here can seriously compromise performance and reliability. Additionally, TSVs can introduce stress that degrades silicon performance over time, especially under thermal cycling.

Thermal management is crucial as high-density interconnects and multiple dies generate significant heat, which needs to be efficiently dissipated to prevent overheating. This requires appropriate thermal interface materials (TIMs). Ensuring interconnect reliability is also tough, as high current densities can lead to electromigration, causing connection failures. Repeated thermal cycling adds stress that can crack interconnects over time.

In assembly and bonding, achieving reliable flip-chip bonding with micro-bumps demands precise control over bump formation, alignment, and reflow. Optimizing the underfill process is critical to protect solder joints from environmental stresses.

Managing yield and defects throughout the stages of lithography, etching, and bonding is vital, as any defects can significantly affect production efficiency. Environmental concerns like moisture sensitivity and outgassing must be managed to ensure long-term reliability. Finally, balancing cost and scalability is essential. Advanced packaging processes are inherently complex and expensive, requiring constant innovation and collaboration to maintain high yield and commercial viability.

These issues impact yield and introduce latent defects. Variations in these processes can lead to electrical performance issues, misalignments, and stress-induced failures, which are difficult to detect during Automated Test Equipment (ATE) testing. Defects like delamination, warpage, and electromigration often manifest under operational stresses, making early detection and effective fault isolation challenging, ultimately affecting the overall reliability and yield of the devices.