Through the Glass: Why the Rapid Development of TGV Demands Rigorous Analysis
Pete Singer
3 days ago
MONITA PAU, Onto Innovation with LPKF Laser & Electronics SE
The drive for increased performance is enticing some advanced packaging manufacturers to transition from traditional organic substrates to glass core substrates, a switch that comes with numerous benefits. Compared to organic substrates, glass core offers superior mechanical strength, is better suited for large package sizes, provides improved electrical properties, and has the ability to meet new line/space requirements of 1.5µm and below in support of the dense interconnects for advanced logic nodes and high-performance packages (FIGURE 1).
 Figure 1. Roadmap for organic and glass core substrates.
Glass substrates, however, are not immediately poised to push aside organic substrates as the preferred material for advanced packaging substrates. Thanks to a host of innovations, organic substrates will remain viable for advanced packages. Regardless, many manufacturers are developing glass substrates now instead of waiting for organic substrates to reach their line/space endpoints.
To optimize this transition from organic to glass substrate, interconnect technologies are changing as well.
Through glass vias (TGVs) are the critical vertical electrical connections that pass through a glass substrate. They require ultra-precise processing, which leads to several obstacles which must be overcome. Glass is brittle, after all, and this creates handling challenges, along with many other potential issues across the fabrication process. Each step—from laser modification on the panel to wet etching, metallization and planarization—opens the process to a host of potential errors, including cracks, critical dimension variation, incomplete debris removal, voids, overfill, and over-polishing (FIGURE 2). Cracks, in particular, are problematic. A small crack early in the process has the potential to grow into a much larger, potentially “killer” defect later and affect the performance and reliability of the end product.
Figure 2. TGV Defect Examples (a) Missing TGV, (b) Incomplete TGV, (c) TGV crack after metallization.
These TGV process control challenges are not limited to cracks. The position accuracy of TGVs is vital for reliable electrical connections between the front and back of the glass substrate. Even slight misalignments can lead to signal integrity issues or device failure. In addition, the shape and size of the vias is another area of concern; as a result, the critical dimensions (CD) of these vias must be tightly controlled. The relationship between the top, bottom, and waist diameters of a TGV determines the profile of the via. Moreover, if the sidewall is too steep or reentrant (narrower at the bottom), it can affect the plating process, leading to incomplete metal-filled vias or voids, impacting the electrical signal performance and reliability of the final device.
Today, manufacturers are adopting a number of best practices to optimize the TGV process. On the incoming quality control front, proper process control includes identifying any defects on the surface in bulk of the incoming glass substrate and determining the thickness uniformity of the glass. Following each step in the TGV fabrication process, measuring critical dimensions after each process step is of imminent concern. Controlling for each of these is critical to maintaining the integrity of the final product and optimizing yields.
In this article we will detail the entire TGV manufacturing process, starting from a bare glass panel and moving on to the fabrication of the via, TGV Cu plating, and TGV chemical mechanical planarization (FIGURE 3). As we discuss the process, we also will address the challenges manufacturers face at each step and expand on a unique ultra-fast laser drilling technique called laser-induced deep etching (LIDE®) that is used in the creation of vias. Afterward, we will move onto the process control solutions that enable manufacturers to reach and maintain high volume production.
 Figure 3. The TGV manufacturing process.
Click here to read the full article in Semiconductor Digest magazine.
PS
Best Chip days still ahead.
Bits ONLY soar from here. Very precise bits. High performance/low watts very complementary.
ASML
Village. |
