Hi Harry
You need to take a hard look at the total heat that is being generated and then work from the allowable jucnction temperature of the LED. Each junction from the LED die inside the plastic package to the ambient free flow air has a thermal resistance. The resistance is quoted in terms of watts per degree temperature rise. Your thin copper laminate of the PCB will have a high value of thermal resistance from the LED mounting flange (if I can call it that) out to the free air. Mounting several LED modules on the same piece of PCB will mean using more area of PCB per LED than would be require for a single LED multiplied by the number of LEDs. Clamping the LED packages to a solid metal surface will help but you MUST ( yes absolutely must!) calculate the heat dispersal capability of your heat sink to see what the LED junctions are going to be ok. You care to look at the mounting methods used by some of the 3 watt plus LED's from other sources. You can get a rough guide as to the size of metal heat sink required from the total wattage assume a 50 degrees ambint for passive cooling and a further 20 degrees from the heat sink mounting flange to the LED inside its package. Thus for 30 watts of LED you are looking for a heat sing with a thermal resistance of 0.43 watts per degree centigrade. To give you an idea of what would be required for the hyperthetical example look at page 19 heat sink part number SK507 and don't neglect the use of thermal paste between the LED mounting flange and the heat sink.
http://docs-europe.electrocomponents...6b80d520d8.pdf
Not exactly compact so you may need to go the forced air route.
The tabs on the LED packages are designed for surface mount but with a little cunning can be used to directly mount to a suitably profiled heat sink whilst preserving the insulation and isolation required to satisfactorily meet the operating conditions for each device.
Hope this helps before you start to test as you could blow the LEDs if you over heat them.
Also the drive conditions may require you to provide separate power supply sources for each LED package particularly if you need equality in light output from each source.
Regards
Pat