Samsung is having some trouble identifying what went wrong with the Galaxy Note 7, which earlier this year was recalled due to a high number of battery explosions, but someone else believes they have the answer. Manufacturing engineering company Instrumental has performed a teardown of the device, and found that the battery simply did not have enough physical room for error.

The problem had more than one factor, the teardown found. A phone battery is made up of positive and negative layers, with separators to keep them from touching and sparking. In order to streamline the size of the battery and maximise space, these separators may have been too thin. Moreover, Samsung made the battery thinner, removing thickness margins.

When batteries are charged, they swell a little. Around 10 percent extra space is required, but the battery entirely filled its 5.2-millimetre-deep pocket, with very little space around the edges. Add the normal pressures of day-to-day handling, and the risk of explosion goes up.

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“Looking at the design, Samsung engineers were clearly trying to balance the risk of a super-aggressive manufacturing process to maximize capacity, while attempting to protect it internally,” the teardown reads. “Samsung took a deliberate step toward danger, and their existing test infrastructure and design validation process failed them.”

You can read the full teardown here.

This article was originally published on CNET.com.