Integrated circuit modules made in accordance with the methods of the present invention have multiple Ball-Grid Array (BGA) packages mounted to a substantially planar support substrate. Each package is inclined at an angle to the support substrate and partially overlaps another package. The first package or row of packages overlaps a wedge that is provided for support. A flexible substrate is mounted to each BGA package and has a portion that extends away from the package to adhere to the support substrate, for communication between each package and signal lines on the support substrate. Optionally, a portion of the substrate that extends away from the integrated circuit package can be bent back at a 180° angle to allow the pads on the top surface of the flexible substrate to attach to mating pads on the support substrate. Precise control of the impedance of select signal traces is accomplished through the use of ground traces that run parallel with the select signal, a ground plane layer, and alternating signal-substrate mounting pads with GND-substrate mounting pads. One aspect of the present invention has the package leads located in close proximity to one side of the package for optimally short trace lengths. Another aspect provides a method for routing signals for optimal signal length and elimination of stubs. A preferred embodiment of a flexible substrate has an accordion portion formed in the flexible substrate to provide elasticity for preventing stretching and distortions of the flexible substrate during automated assembly. A method is provided for connecting signals lines of each flexible substrate in series. Various embodiments of package lead mounting pads formed in the flexible substrate that provide electrical and thermal coupling to package leads including ring-shaped pads, flexible tabs, and apertures for removing flux, excess solder, and debris.