Multiple LED matrix array circuit boards are pieced together a form a display panel. L-shape brackets are mounted on the bottom sides of the circuit boards and aligned with the butting edges of the circuit boards. The vertical butting walls are pressed together by clamps. A set screw is inserted in one jaw of the clamp to tighten the pressure between butting edges of the circuit boards. Another set screw is inserted on top of the clamp to align the adjacent boards vertically.