Glass Core Substrate Sample Preparation

The "Glass Core Substrate" in semiconductor advanced packaging relies on TGV (Through-Glass Via) technology combined with copper metallization for redistribution layers. It replaces the core layer of traditional ABF organic substrates with glass, eliminating warpage in large AI chips at elevated temperatures while pushing line width and pitch down to the micrometer scale.

Its primary application is the advanced packaging of AI/HPC server chips, where glass core substrates replace the conventional ABF organic core layer to address high-temperature warpage and high-speed signal integrity issues in large-scale chips. Through TGV glass vias serving as interposers, glass bridges, and temporary carriers, vertical high-density interconnects between chips are achieved. Meanwhile, glass-based metal circuitry — already mature and mass-produced in display panels (OLED/LCD driver electrodes, color filters) — has extended into MEMS sensors, microfluidics, biochips, RF devices, and automotive electronics, where insulation, transparency, low dielectric loss, and high reliability are required.

The key challenges in preparing such samples are threefold: (1) glass is inherently brittle — conventional abrasive saw cutting easily causes edge chipping and cracking, and can lift the micrometer-scale metal film on the surface; (2) the significant difference in removal rates between soft glass and hard metal causes step formation on both sides of metal lines during grinding, creating a "relief effect" that obscures the true interface; and (3) the weak adhesion between thin films and the substrate means even moderate polishing pressure can cause delamination or missing segments in the circuit pattern.

The corresponding approach is as follows: cutting is performed with a diamond precision cutting machine at low feed speed with water cooling to flush away debris and suppress chipping; mounting uses vacuum-cold-cast epoxy resin, with edge sealing applied first to reinforce the specimen before full encapsulation, thereby avoiding thermal-stress micro-cracking; grinding and polishing proceed through coarse grinding, fine grinding, and progressive polishing stages, using diamond suspension on velvet polishing cloth under low pressure in graduated steps, and finishing with colloidal silica final polish to completely remove the surface deformation layer — thereby revealing the true morphology of the glass-to-metal interface.

Sample preparation parameters and metallographic results are shown below:

1. Coarse Grinding: DiaRe P800–2500;

2. Coarse Polishing: SC polishing cloth + 3 µm PD-WT polycrystalline diamond suspension;

3. Final Polishing: ZN polishing cloth + 50 nm SO-439 polishing suspension.