To tear down the iPhone 4S (or 4), it is necessary to remove two screws from its bottom side first. However, we realized that we did not have a screwdriver to do it. The iPhone 4/4S uses screws with star-shaped holes (Torx) so that it cannot be easily disassembled. But all of the Torx drivers we had were too large to fit the screw heads.
Though we we regretted that we had not prepared for the teardown well as in the case of the teardown of the "iPad 2" tablet computer, whose front glass was cracked, there was no other way to continue the teardown than to remove the screws.
"When we broke down the iPhone 4 before, we inserted a flat-blade screwdriver into its screw heads and turned the screws by sheer force," said one of the participants in the teardown. So, we decided to try this method.
First, we used this method on the iPhone 4, and its screws were removed more easily than we expected. So, we thought it would be easy to take out the screws from the iPhone 4S, too, but it turned out to be wrong.
No matter how much force we applied, the screws were not turned by the flat-blade screwdriver. The more force we applied, the more the screw heads became worn. But, in the meantime, the screw heads began to gradually come up. So, we finally removed the screws by turning them with a nipper.
The Nikkei Electronics Teardown Squad gave up after taking out one screw, and the other screw was removed by an engineer who works for a parts manufacturer.
When we compared the two screws removed from the iPhone 4S and those of the iPhone 4, it seemed that more thread lock agent (blue) was used for the iPhone 4S' screws than for the iPhone 4's screws. Probably, this is the reason why the iPhone 4S' screws were harder to be removed. In consideration of the use of the agent and Torx screws, we felt that Apple Inc did not want to make it easy to open the chassis of the iPhone 4S.
Once the screws were taken out, it was easy to remove the back cover. When we compared the iPhone 4 and 4S after removing their back covers, we noticed that the arrangement of the iPhone 4's components and that of the iPhone 4S' components were very similar. But, at the same time, we felt that something was different.
"The widths of their batteries are different," an engineer said.
After removing the lithium-ion (Li-ion) rechargeable batteries from the phones, we found that the width of the iPhone 4S' battery was about 1mm smaller. Because battery capacity was increased from 5.25 to 5.3Wh, we thought that the thickness of the iPhone 4S' battery was larger than that of the iPhone 4's battery.
So, we measured their thicknesses with a caliper but found no difference. Probably, Apple increased battery capacity by making improvements to the electrodes and the electrolyte.
Because the width of the new battery is smaller, the width of the iPhone 4S' main board is larger than that of the iPhone 4's main board. Actually, the iPhone 4S' main board is completely different from the iPhone 4's main board.
For example, Apple replaced OmniVision Technologies Inc's 5-Mpixel image sensor used for the camera module with Sony Corp's 8-Mpixel image sensor. Though the speaker-related components were not changed much, most of the other components were quite different from those of the iPhone 4.
Correction Notice: Because of a reporting error, we incorrectly stated "Apple replaced OmniVision Technologies Inc's 5-Mpixel camera module with Sony Corp's 8-Mpixel camera module" in the last paragraph. In fact, "camera module" should have been "image sensor used for the camera module."