How to update BIOS by using USB memory stick? Secureboot and UEFI is required. I need to update BIOS to about 100 Thinkpads.

I have 50 USB sticks which I will clone.

1. Download 'BIOS Update Utility (Windows)' from Lenovo website.

2. Run the file and choose 'Extract Only'

3. From extracted folder, open 'Instruction US - BIOS flash USB memory key.txt'

HOW TO CREATE A BOOTABLE BIOS FLASH USB MEMORY KEY

1. Attach a USB memory key to your Windows system, then format the USB memory key.
   Note: A medium formatted with NTFS or exFAT is not supported by this Flash Update process.
         Use FAT32 or FAT16 as a file system of the medium.
2. Open command prompt with administrator right, then move to a directory of this
   package.
3. Run mkusbkey.bat in the directory with following command format, then finish 
   creating BIOS flash USB memory key.

        Syntax : mkusbkey.bat [Drive]

        [Drive]
                D:,E:,F:... : Drive letter assigned to the USB memory key

  Example : mkusbkey D:

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HOW TO UPDATE BIOS AND EC FIRMWARE BY BIOS FLASH USB MEMORY KEY

1. Make sure that a system main battery is fully charged and AC power is
   attached. On tablet system, attach an external keyborad.
2. BIOS Setup item Startup->UEFI/Legacy Boot needs to be "Both" or 
   "UEFI Only"
3. Attach a BIOS flash USB memory key to the target system.
4. Power on the target system, then press F12 key to show Boot Menu.
5. Select USB HDD in the Boot Menu, then press Enter to make the target system
   boot from the USB memory key.
6. BIOS/EC firmware update process will start. Please proceed according to the 
   display on the screen. System will reboot several times and actual firmware 
   update process will occur during these system reboot events.
   Do not power off the target system during these system reboot events to 
   complete firmware update process until operating system boots up. 

3. Open command prompt with admin rights, cd to extracted folder and run command

mkusbkey.bat [Drive]

[Drive] is  the letter assigned to the USB memory key, eg.  D:, E:, F, ....

I used 1 GB USB stick.

4. In Linux I created a image file from the USB stick by running

sudo dd if=/dev/sdb of=LenovoUSB.img bs=1M

where sdb is the USB stick.

5. I used USB Monster (https://github.com/digabi/usb-monster/tree/master/src) to simultanously write the image to 20 USB sticks. I have two ten port USB hubs.

sudo ./write_dd.py /home/user/LenovoUSB.img