I was interested in AEHR Test Systems. I wondered why there doing so well, and how their technical moat protects them. Before I get started, I thought I’d discuss their overall testing. AEHR does burn in testing. The test evaluates how much voltage the semiconductor can take before it starts to breakdown at a high temperature. The test identifies defective chips before they are mounted on leadframes (the electrical connection to the mother board or assembly), coated with plastic, and subjected to further testing. The sooner the defective chip is identified, the less time and material is wasted on it. This also gives valuable feedback to the semiconductor foundry so that they can optimize their processes. The critical part of their businesses is their multi wafer testing units. They do make testers for individual microchips and for electronic assemblies, but their equipment that adds unique value for their customers are their burn in wafer equipment.
AEHR systems has three multi wafer streams of revenue:
FOX-XP Multi wafer Module Test System: This test system hands 18 x 300 mm wafers at a time. This system works at higher voltage (29V) or high current 2A and higher temperatures, 300F, than their competition. This is important because silicon carbide chips used in electric vehicle inverters. These chips are 3X as expensive than Si, but they enable batteries to be charged faster and with more energy than silicone chips allow. The silicon carbide chips are expensive because the process to make the ingots is creates more defects in the base material than found in silicon ingots. Those ingot defects cause more malfunctioning silicon carbide chips to be created. Creating an 300F with oven with good temperature control and working with 2A is no big deal, but the chassis that allows the test surface to remain aligned with the wafer and the mechanical transport of the wafers is key to this unit. When this unit is used to test silicon carbide, it has to run for 96 hr. with a lot of expansion and contraction on a microscale occurs. There’s a lot of software and electrical test connections to identify the malfunctioning chips, but that isn’t the key to the moat. The test is covered by US 7826995 B2 and the patent application US 7826995 B2 with updated information.
FOX-XP WafePak Contacter: This unit is a contact surface that provides a contact point for every 1.4 square millimeters. EVERY chip on wafer is tested. The contact surface has to have precision fabrication and have precision placement. Placement is done offline, which I will discuss below. The layout of the contacts is covered in design patents US D875579 S, US D850309 S. The test surface is covered by US 7826995 B2 and its manufacture is covered by US 7762822 B2. Importantly, the surfaces needed to be replaced often, and it is a consumable portion of the business. The design allows the wafer to remain in contact with the tester at higher temperature and under higher volage conditions which allows for the testing of silicon carbide. AEHR guessed right about this technology and made sure their equipment covered this the temperatures and voltage ranges for silicon carbide, so this is a pretty big advantage.
Automated FOX-XP WaferPak Aligner: Automatically aligns up to 50 x 300 mm wafers using optical alignment and placement in a WaferPak contactor. A lot of the design for all three systems is covered in two new applications US 20230168277 A1 and US 20230168277 A1.
Based on what I read I think that AEHR has 3 protected advantages, best in class alignment of their test surface, the ability to test higher temperatures and voltages for silicon carbide chips, and the lowest cost system on a throughput basis.
I’ll take a look at the business results, and if those look good, I’ll probably open a small position in AEHR.