I did battle most of the day with the DesignSpark PCB tool attempting to get a good quality board designed. A reasonably large board, 4 x 6", less than 40 components, and building it as a four layer board, which shouldn't be challenging. However, I may have to hand route everything.
I finally spotted a problem, that the ground and power planes in the four layer board weren't being used for ground and +5V. That cut down on routing and had the added advantage of handling the fairly beefy current requirements of the peripheral driver chips, which can sink 150ma per signal line when it has a logical 1 value. The worst case is during a seek command, with multiple track lines active plus the strobe.
The next step was some intelligent placement of the components, knowing how they need to be routed, to minimize crossing paths and conflicts. The pull up and pull down resistors that form the terminator for the input signals were the major factor in congestion, thus they were the major focus of my work.
I also moved the filtering capacitors and the peripheral driver chips to make more room for signal paths on the board. The result was a good clean routing with no manufacturing check conditions. With that complete, I produced the outputs needed for board manufacturing - gerber and excelon format files for the various layers and drill holes.
I will order two boards and enough components to build 4 or more boards- connectors, chips, resistors, and capacitors, which will let me complete the boards once everything gets here.
The foundry I chose, 4pcb.com, has a free service to analyze the files for manufacturability issues. I made use of it and found quite a few niggling errors and one significant one that slipped past the design checks of the DesignSpark PCB software. Time to iterate until I get satisfactory results from the foundry's free check software.