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Comment by tiffanyh | Hacker News Reader

Thermal Conductivity

I wonder if this is related to the use of Titanium and the poor thermal conductivity of Titanium (17 W/m-K) vs. Aluminum (210 W/m-K).

Aluminum dissipates heat more than 10x better than titanium.

https://waykenrm.com/blogs/titanium-vs-aluminum/#:~:text=All....

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EDIT: I no longer think it's thermal conductivity due to the change in metals. See below.

https://news.ycombinator.com/item?id=37705152

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The amount of titanium in the iPhone is about a 1-2mm band around the outside. The inner chassis is still aluminum, and they are diffusion bonded together. While that Ti is at the primary thermal boundary for the metals in the phone, I would guess (judging from experience with both stainless steel and titanium banded phones) that most heat escapes through the glass front and back of the phone, even though they have poor conductivity.

>...most heat escapes through the glass front and back of the phone, even though they have poor conductivity.

Some does, but given glass' very poor thermal conductivity (1.38 W/(m·K)), heat dissipation by the band around the outside is probably a very significant factor in total heat dissipation.

There is usually a rubber case around all of the metal, so I do think that phones should be able to operate only with heat escape through the front glass alone.

Right, but the surface area of the glass and the proximity to the heat source more than make up for this. Just hold a phone under load and it’ll be obvious.

I’m sure Apple has much more in depth studies of the thermal characteristics of their product than I can armchair analyze, though.

> The amount of titanium in the iPhone is about a 1-2mm band around the outside.

Just to confirm, it’s almost exactly 1 mm, and the aluminum part it’s welded to adds about another millimeter: https://youtube.com/watch?v=S_W73ouKtjU&t=9m44s

(That’s for the Pro Max. The Pro could conceivably be slightly less.)

> Ming-Chi Kuo, an Apple analyst at TF International Securities, said any overheating issue was probably due to “compromises” in the phone’s design as the company attempted to reduce the product’s weight.

> The iPhone Pro model has a frame made from titanium, a poor conductor of heat, which could hamper the handset’s ability to disperse heat. Previously, Apple has used stainless steel for its high-end phones.

> Previously, Apple has used stainless steel for its high-end phones.

I saw that too. I thought Apple mainly used aluminium?

Well, it's not Thermal Conductivity then.

I just looked it up.

  Stainless Steel   15 W/m-K
  Titanium          17 W/m-K
  Aluminum         210 W/m-K

Effectively, Stainless Steel & Titanium have the same thermal conductivity.

https://www.hardrok.com.au/thermal-activity-in-stainless-ste....

The issue here is users complaining that the phones get too hot to handle, which immediately eliminated conductivity. A thermal conductivity problem would've looked like the phone overheating without the outside getting too hot to handle. (picture the circuit board inside a thermos)

that's not necessarily true. Heat has to go somewhere eventually. It could be that the CPU is much hotter than the temperatures felt on the frame. but yea, if the cpu is 45 C and the frame is 40 C, you'd be right.

The interior has been aluminum, but the band around the outside has been stainless steel.

> Ceramic Shield front, Textured matte glass back and stainless steel design

https://support.apple.com/kb/SP875?viewlocale=en_US&locale=e...

Interesting. 13 mini is

> Ceramic Shield front, Glass back and aluminum (sic) design

https://support.apple.com/kb/SP847?locale=en_GB

The previous generation of iPhone Pros used stainless steel instead of Titanium.

Which, at 15 W/mk, is even worse than titanium.

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