13 May Tesla’s Screen Saga Shows Why Automotive Grade Matters
Every bit of Tesla-related news and analysis tends to get sucked into the polarized debate over whether Tesla is the greatest company ever or an irredeemable fraud, which is a shame considering there are far more interesting and valuable insights to be gleaned from the company’s experience. After all, this is the first time that Silicon Valley’s move-fast-and-break-stuff approach has been applied to the methodical, measure-twice-cut-once auto industry and with more high-tech firms moving into mobility it’s important that the right lessons are learned.
One of the most dramatic illustrations of both the benefits and downsides of Tesla’s approach to automaking comes from its decision to use 17-inch touch screens in its Model S and X. No automaker had ever used a screen even close to as large as the model Tesla used, and it instantly became a symbol of its entire approach to building cars like mobile devices. In the brutally competitive premium car market, the gigantic display became a rare example of a feature that totally differentiates Tesla’s product from even its far newer competitors.
But rarely is the question asked: why haven’t other automakers kept up with Tesla’s competition and installed a similarly massive screen in their cars? After all, if Tesla can buy such a screen from a supplier why can’t Mercedes or Lexus? In order to answer this question, we must turn first to Ashlee Vance’s biography of Elon Musk in which he brags about the process of sourcing the Model S display.
“When we first talked about the touch-screen, the guys came back and said, ‘There’s nothing like that in the automotive supply chain,’” Musk said. “I said, ‘I know. That’s because it’s never been put in a fucking car before.’” Musk figured that computer manufacturers had tons of experience making seventeen-inch laptop screens and expected them to knock out a screen for the Model S with relative ease. “The laptops are pretty robust,” Musk said. “You can drop them and leave them out in the sun, and they still have to work.” After contacting the laptop suppliers, Tesla’s engineers came back and said that the temperature and vibration loads for the computers did not appear to be up to automotive standards. Tesla’s supplier in Asia also kept pointing the carmaker to its automotive division instead of its computing division. As Musk dug into the situation more, he discovered that the laptop screens simply had not been tested before under tougher automotive conditions, which included large temperature fluctuations. When Tesla performed the tests, the electronics ended up working just fine.
The screen Tesla ended up going with was the Innolux G170J1-LE1, which was designed for industrial rather than automotive applications. As such it was tested to a higher standard than many laptop screens, and its reliability test criteria (found on page 22 of this data sheet for rev C3 of the part [PDF]) might seem impressive to anyone outside of automotive supply chain professionals. Some of these standards include:
- High temperature operation test: +80C for 600 hours
- Low temperature operation test: -20C for 120 hours
- High temperature storage test: +90C for 500 hours
- Low temperature storage test: -40C for 500 hours
- Thermal shock storage test: -40C for 75 min <-> +85C for 75 min; 550 cycles, 1.5 hour/cycle.
Keep in mind that this is a later revision introduced in 2016, whereas earlier versions were slightly less stringent. Turning to the AEC-Q100 standard for automotive grade thermal testing [PDF], we find that the standards for the parts that go into your car are much higher. Here is a quick rundown of a few of the thermal standards:
- Grade 4:
High Temperature Operating Life (HTOL): +90C for 408 hours. High Temperature Storage Life (HTSL): +125C for 1,000 hours. Temperature Cycling: -10C tp +105C for 500 cycles.
- Grade 3:
High Temperature Operating Life (HTOL): +105C for 408 hours. High Temperature Storage Life (HTSL): +125C for 1,000 hours. Temperature Cycling: -50C tp +105C for 500 cycles.
- Grade 2: High Temperature Operating Life (HTOL): +125C for 408 hours. High Temperature Storage Life (HTSL): +125C for 1,000 hours. Temperature Cycling: -50C tp +150C for 500 cycles
- Grade 1:
High Temperature Operating Life (HTOL): +150C for 408 hours. High Temperature Storage Life (HTSL): +150C for 1,000 hours. Temperature Cycling: -65C tp +150C for 500 cycles
- Grade 0: High Temperature Operating Life (HTOL): +175C for 408 hours. High Temperature Storage Life (HTSL): +175C for 1,000 hours. Temperature Cycling: -65C tp +175C for 500 cycles
As we can see, the Innolux screen is tested to roughly the lowest “Grade 4” standard, although even there its high temperature storage testing (as well as high temperatures in thermal cycling testing) falls slightly short. Electronic parts qualified for “passenger compartment hotspots” like a central display are typically tested to Grade 2, which the Innolux would almost certainly fail to pass. Dashboards and center stacks see some of the highest interior temperatures in a car, with +80C easily achieved through solar radiation and ambient temperature alone, and the nearby HVAC unit, the in-car processor for Autopilot and the display processor itselfadding considerable thermal load.
Tesla’s decision to use a large display that wasn’t tested to higher automotive grade standards had fairly predictable results. First the Model S and X screens were
a bizarre problem that was clearly caused by thermal issues: bubbles would form on the sides of the displays and eventually leak a gooey adhesive material into the car’s interior. Tesla appeared to mostly fix this problem with its “cabin overheat protection” feature (which it sold as being to protect dogs and children, despite the fact that it held the temperature at +40C which is about the temperature where a child’s organs will start shutting down) as well as revisions to the Innolux panel. Intriguingly, a blog post at Mentor Graphics suggests that Innolux was struggling with thermal management on a screen for an unspecified “high end automobile,” ultimately concluding that “defining the boundary conditions for Innolux’s system is the responsibility of their customer, not Innolux.”