Layout Considerations

Generally this circuit is fairly free of layout restrictions, however there are some things that you can do to make your life easier. A sample layout is shown below.One of the things to note is that the transistors are arranged "back to back" with their tabs facing each other. In my layout I have spaced them 3/8" apart which allows me to put a piece of 1" x 3/8" x copper bar stock down the middle and with #4-40 machine bolts to secure it. A 1 - 1/2" piece of this stock weighs about 3 oz. This basically doubles to current capacity of the bridge, and if you then bolt the copper bar to a metal enclosure you can triple the capacity to a full 6 amps continuous duty. Further, the two left transistors are the "upper" source transistors and the two right transistors are the lower "sink" transistors. That means that any thermal solution will have heat being injected from diagonal corners which further maximizes the benefit by spreading out the heat injection. The point here is to think about whether or not you are going to put heat sinks on the transistors and lay them out accordingly.
The layout in the zip file is very slightly different than the first run, I added more room for the over-voltage snubber and added a place to put a .01uf capacitor across the motor leads (cuts down on brush noise).
Alternatively you can build this bridge on a piece of perfboard and just solder it together. Be sure and use at least 18 ga wire on the legs of the transistors.