If it is just dirt I usually just use compressed air and a soft bristle brush. As long as the dirt isn't conductive its only real harm is that it can insulate components and not allow them to cool properly and of course the cosmetics of the board. If there is any moisture content I may use some 100% ethanol to bind to the water and pull it out of the cracks and tight areas before I use the compressed air and brush. For the board that you show I suspect that air and brush will work well.
If it is just dirt I usually just use compressed air and a soft bristle brush. As long as the dirt isn't conductive its only real harm is that it can insulate components and not allow them to cool properly and of course the cosmetics of the board. If there is any moisture content I may use some 100% ethanol to bind to the water and pull it out of the cracks and tight areas before I use the compressed air and brush. For the board that you show I suspect that air and brush will work well.
