I can tell you how I did it using "Microsoft Photo Editor" (MPE). I'm sure it's the same with other graphic programs.

First I stole (I mean coped) each scan and pasted them into MPE in separate windows. I then hit the "Window"/"Tile Images" command to show all 12 scans on my screen.

I then selected one scan and hit the "Image"/"Crop" command. I then added a margin of 250 pixels (the width of your scans) to the left and right of the scan. At this point I copied a second scan and pasted into the left margin I just created in the first scan. I then copied a third scan and pasted it into the right margin of the first scan.

The first scan now showed 3 chips. To this scan I added a right margin of 250 pixels and pasted a 4th scan. I think you can see how I can keep adding scans of chips to the first scan by constantly increasing margins -left, right and below.

I reduced the size of the finished scan by 50% and up loaded it to my server. DONE