August 19th, 2019
Grinding is one of the oldest methods of surface preparation in human engineering. In fact, modern grinding wheels that are used to finish extremely hard substrates with sub-micrometer (µm) scales of precision, are based on a simple tool that has existed since at least 830 CE (Common Era). The grindstone is a round block of an abrasive mineral attached to a rotary mechanism – a crank handle or pedal – that causes the stone to spin. A tool could be sharpened by angling the edge into the spinning wheel and applying pressure.
Although revolutionary for its time, the grinding wheel was quickly superseded during the early days of the first Industrial Revolution. The first conventional grinding wheel was built of wood embedded with particles compounded of iron and corundum, known as emery. While useful for surface preparation beyond sharpening, there were significant cost and quality issues associated with importing emery from overseas.
The next great stride in grinding wheel manufacturing followed the discovery of two abrasives that are still widely used in substrate surface preparation today: aluminum oxide (Al2O3), and silicon carbide (SiC). Effectively implementing these hard-wearing abrasives in surface preparation tools required a fundamental re-think of the grinding wheel process. The solution was one of the earliest forms of composite materials.
In wood and emery grinding wheels, the abrasive particles were bonded to the wooden wheel using a rubber- or clay-based adhesive. This contributed to gradual clogging which was difficult to reconcile. Using refractory abrasives like aluminum oxide and silicon carbide, manufacturers could disperse the abrasive aggregate in an adhesive matrix and fire the raw composite to manufacture a grinding wheel that would deliberately and gradually erode. This method of erosion would continuously present a fresh cutting face for longer service in substrate surface preparation.
Although a common fixture in most machine workshops since the turn of the 20th Century, those grinding wheels have since been succeeded by the onset of superabrasives. These are grinding tools which use diamond or cubic boron nitride (CBN) as the abrasive within the wheel bond, which – alongside grain size and spacing – determine the wheel grade from A – Z.
Tight control of each of these parameters is essential for reaching the levels of precision required for advanced substrate surface preparation. The success of ceramic and semiconducting wafers can hinge on micro-scale topographical uniformity and planarity. Tiny metrological variations can inhibit critical qualities for downstream applications and require costly re-finishing steps that can easily be avoided with cutting-edge products.
With careful control of the abrasive grain coarseness and density within the wheel bond, it is possible to develop grinding wheels with extremely fine finishing tolerances. This enables the development of back and edge grinding wheels for high-technology electronic substrates.
Saint-Gobain Surface Conditioning is a world leader in particle engineering for substrate grinding and finishing applications. We have significant expertise in grinding hard-to-work substrates like Silicon Carbide (SiC), sapphire, aluminum nitride (AlN), gallium nitride (GaN), silicon (Si), silicon nitride (SiN), and more.
If you would like to learn about our grinding products for electronic substrate surface preparation, simply contact a member of the Saint-Gobain team today.