I’ll share my solution in case anyone else runs across this later. I had a 3x3 matrix made out of nine ElectroMage 8x8 LED Matrix (SK6812) boards (I love these boards, they are so bright and easy to work with!). I wanted to leave room for an expansion of seven more boards to make a 4x4 matrix later on.
I carefully planned out a design of “popsicle sticks” or craft wood sticks (114mm x 9.6mm x 2mm) that would allow for room around the 3-pin header connections. I also wished to have each stick make contact with two or more boards and reinforce each other. Working with one row at a time I used some heavy T-squares to keep things aligned. I used Gorilla Glue Super Glue Gel, which I love for projects as the gel formula stays where you put it and won’t run all over. I would glue a stick into place and then weight it down to ensure good contact while I moved on to the next stick. I included a place to attach a stand to the bottom of the completed matrix and also a place to hang it on a wall at the top of the matrix (I hadn’t decided on a placement yet)
I had some 8 inch / 20 cm Dupont jumper cables ( see Amazon.com ) which were the ideal length and connector to wire all the boards together.
If you’ve any questions, I will try to help!