A report by research group IHS in 2012 found that only 11.3 per cent of electronics component manufacturers provided such data but companies such as Samsung and LG have recently stepped up their efforts to detail sourcing. Last month, Intel said that it was manufacturing the first micro processors with validated conflict-free gold, tin, tantalum and tungsten.
Elsewhere in its annual Supplier Responsibility report, Apple said that95 per cent of more than 1m of its suppliers' workers adhered to a maximum 60-hour work week, up from 92 per cent a year ago.
After the 2012 audit found more than 100 instances of underage labour in 11 of its suppliers' facilities, Apple last year found 11 active cases and 12 historical cases of children under 15 working in eight facilities.
Mr Williams said that these improvements were accompanied by wider education of health and safety and working conditions among its suppliers.
"We'd like to drive [working hours compliance] up above 95 per cent butthe right answer is close to somewhere where we are," he said. "I don't think asingle week here or there where someone works longer is the end of the world…The real win is to go deeper in the supply chain and find more and more places where 70-80 hours a week is the norm and get those pulled in line."
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In a report published in December, the Fair Labor Association, which has worked with Apple in the past to audit its suppliers, found that Foxconn had implemented 356 of its 360 recommendations to improve working conditions at three Chinese factories making Apple products.
The FLA found that "steady progress" in terms of working hours had beenmade at the facilities, which it estimates employ 170,000 workers, but noted that they were still "not in compliance with Chinese labour law regarding hours of work".
Carolina Milanesi, a mobile industry analyst with Kantar Worldpanel, said: "We've definitely seen an increase in the level of detail and the focus[Apple] put on this sort of thing since Tim [Cook] became chief executive."
Mr Williams now holds most of Mr Cook's former duties as chief operating officer, having been promoted in 2010 after 16 years working at Apple.
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