After analyzed the Samsung Galaxy Note 7 by the Engineers over at Instrumental Technologies and revealed the exact reason why the phone’s battery exploded.
Due to put things into simple terms, the Samsung Galaxy Note 7 failed due to improper tolerances. In engineering and manufacturing, tolerance is the acceptable deviation in any magnitude, so in this case the space between objects. This is to ensure a good fit manufacturing, to ensure product reliability and safety or to compensate for variation in component size when under different thermal (or other) loads. In simple terms, tolerances are in place to ensure that a device works within its intended specifications.
Traditionally when the dimensions of a component move beyond a certain tolerance when they are under thermal loads (become too big or too small when they are hot or cold), they are rejected or marked as non-compliant. In the case of the Samsung Galaxy Note 7, the battery was placed into the with very close tolerances, with the battery being as close as 0.1mm to the rest of the phone in some cases never further than 0.5mm fro the edge of the batteries CNC-machined battery pocket.
When the phone goes under load several parts of the phone increase slightly in size, including the battery, which means the phone was able to exert pressure on the battery & allowing the battery’s positive cell layer and negative cell layer to be squeezed closely together. When this happens the insulation material between these two layers becomes useless and energy can be fed from one layer to the other, causing a ramp up in temperatures and a huge fire-risk.
The reason of failure of the Samsung Galaxy Note 7 was due to Samsung placing a large battery into a compact space, leaving minimal design tolerances in the X and Y axis (Less than 0.1mm in places) and almost no room in the Z-axis where a typical allowance for a battery is 10%.
Samsung uses a 3,500mAh battery for the Note 7 to give it a competitive battery life, though it is thought that this would have lead to failure even if the “explosion” issues didn’t occur. Over time the battery in the phone would have expanded, resulting in a phone which would have warped and changed its shape as a result, which again is a negative outcome for Galaxy Note 7 users.
Instrumental Technologies deemed that the Samsung Galaxy Note 7 would need to use a battery that was smaller than both the Galaxy Note 5 and iPhone 7 Plus which will be safe for use, making the devices’ battery life short and not competitive in the modern marketplace. In the eyes of the engineers at Instrumental Technologies, the design of the Note 7 has “no competitive salvageable design”, effectively making the phones design a dead weight for Samsung.