Samsung has completed its investigation of the Samsung Galaxy Note 7, concluding that two seperate battery construction issues were the cause of the phones exploding and catching fire.
This official announcement comes one week after a Samsung insider said that the firm was blaming the battery.
The company used two suppliers for the Galaxy Note 7: Samsung SDI (a sister company in Samsung Group), and Amperex Technology Ltd (ATL). The report says that both had issues, though it only refers to the battery manufacturing partners in vague terms – i.e. 'Battery A', 'Manufacturer B'. However, Samsung identifies 'Battery A' as "from the first recall," and the first recall exclusively targeted batteries made by Samsung SDI.
For the Samsung SDI batteries, the investigation found that the corner of the battery casing was too small, resulting in the negative electrodes in the corner of the battery being bent, which in turn made it easier to short-circuit the battery and cause a "thermal runway" situation where the battery explodes. Consulting company Exponent, which helped in the investigation, said that this "unintended damage was present in all of the cells examined by Samsung and Exponent". This effectively means that pretty much 100 per cent of the initial batch of Galaxy Note 7s were defective. Samsung also identified "an additional contributing factor" with Battery A – the negative electrodes were too long, which led to them being bent in the curve on the battery's long side.
'Battery B' – which previous reports said was manufactured by ATL – was used in all the replacement Galaxy Note 7s. It didn't have any of the defects found in Battery A, instead having its own welding problem. When connecting the positive tab to the battery, "Manufacturer B's" welding process – called "poorly controlled" by Exponent – created sharp welding burrs. Batteries will contract and expand during charge and discharge, but in the case of 'Battery B' the high, sharp burrs would scrape against the insulation between battery layers and eventually lead to penetration of that insulation and combustion. Another "additional contributing factor" towards 'Battery B's failure was that some of the batteries were missing insulation tape which helped to reinforce certain trouble spots.
The company said that "approximately 700 Samsung researchers and engineers replicated the incidents by testing more than 200,000 fully-assembled devices and more than 30,000 batteries". It also hired three external consulting firms: Underwriters Laboratories (UL), TÜV Rheinland, and the aforementioned Exponent consulting.
In the wake of the report, Samsung says it has "reassessed every step of the smartphone manufacturing process" and that it has come up with a new "eight-point" battery safety check process including the same investigative techniques that helped solve the Note 7 defects. These steps include factors such as the use of an X-ray machine, and physically disassembling the batteries to look for problems. The company has also "formed a Battery Advisory Group of external advisers, academic and research experts to ensure it maintains a clear and objective perspective on battery safety and innovation".
Before the announcement of the report's findings, Samsung Mobile president DJ Koh said: "I deeply apologise to all of our customers, carriers, retail and distribution partners, and all of our business partners."
The Galaxy Note 7 was cause of the company's biggest ever recall, with the company recalling it twice and eventually shelving the device. Samsung confirmed in October that it was to carry out an investigation into the debacle.