Suppliers of displays to Apple Inc. (NASDAQ:AAPL) are struggling to get enough screens ready in time for the upcoming iPhone 6 launch after a component redesign set back production, according to a new report Friday.

The iPhone 6, which is expected to be available in two bigger screen sizes, measuring 4.7 inches and 5.5 inches, is now awaiting the redesign of the backlight, which helps illuminate the screen. The overhaul apparently led to a setback in the production of display panels, putting on hold the screen-assembly process for some time between June and July, Reuters reported, citing “two supply chain sources.”

According to one of the sources, Apple initially aimed for a thinner form factor and wanted to have a single layer of backlight film, instead of the usual two layers, on the 4.7-inch screen version. But, the company later realized that the new configuration would not make the screen bright enough and sent the backlight back to get the extra layer.

Although the entire process temporarily slowed down screen-assembly operations, suppliers are now working hard to compensate for lost time, Reuters reported. Japan Display Inc (TYO:6740), Sharp Corporation (TYO:6753) and LG Display Co Ltd. (NYSE:LPL) have been selected to make the iPhone 6 screens, according to Reuters.

Meanwhile, the production of sapphire covers for the 5.5-inch iPhone 6 is reportedly on track, and GT Advanced Technologies Inc (NASDAQ:GTAT) is estimated to supply enough sapphire to produce covers for 1.35 million to 2.25 million units of the handset by the end of 2014, DigiTimes, a Taiwanese news website, reported on Friday.

The report also stated that a 5.5-inch sapphire screen cover is estimated to cost $100, which is considerably more expensive than covers made from reinforced glass that cost between $5 and $10.

Meanwhile, another DigiTimes report claimed Friday that Samsung Electronics Co Ltd (KRX:005930) is back on Apple's list of suppliers for mobile RAM chips for the iPhone 6, which is expected to be released in mid-September.

In 2013, Apple stopped buying many components from the South Korean company, including application processors, mobile RAM, NAND flash chips and batteries. However, the iPhone-maker was forced to depend on its biggest rival for the mobile RAM yet again after existing suppliers, such as SK Hynix and Elpida Memory, failed to ramp up supplies of the component, according to DigiTimes.