Metal Core (MCPCB)
Variety of Aluminum and Copper core in inventory
Heat transfer simulation and analysis
Multi layer MCPCB and thermal stitching
LED application with a demanding heat transfer profile are best solved and service with pedestal MCPCB technology. The Pedestal MCPCB construction is allowing the designer to get a direct path between the LED (heat generator) to the metal core of the PCB.
The cross section of the std single layer MCPCB – Copper or Aluminum – is always a metal core ( Aluminum or copper), a thin thermally dielectric layer and the copper foil.
When the LED is soldered onto a copper foil the dielectric layer between the copper foil and the metal core (Aluminum or Copper) acts as a heat barrier. For this reason there are so many options of dielectric thickness and conduciveness in order to reduce the effect of the dielectric on the flux of heat from the LED to the PCB metal core.
However, there are scenarios where the application where this is not enough and only a direct heat path between the LED and the metal core of the MCPCB will allow sufficient cooling of the LED. This is where the Pedestal ( pillar ) construction is very useful.
The pedestal design is based on MCPCB with a copper core and not Aluminum. The reason for that is that aluminum can not be soldered to and the idea is to have the LED (heat generator) be soldered directly to the copper based of the MCPCB.
When the pedestal is done right it will look like any other pad on the PCB from the top side of the PCB.
MCPCB with pedestal cross section
MCPCB construction compared with regular FR-4 already introduces cost increase and the pedestal technology is an additional increase on top of that. One way to offset some of the additional cost associated with the pedestal construction is not to use a thermally conductive dielectric. This make sense in most cases because the pedestal is already addressing the heat path between the heat generator (the LED) and the copper core.
To benefit from this ultimate heat transfer from the LED to the Copper base the LED packaging needs to have a thermal pad.
Design Rule for 1Oz Finished Copper
Spacing & Physical Design Rule
| Sl.No | Item | Min: Rule / Standard |
| 1 | Traces to traces | 4 mil (0.1 mm) |
| 2 | Traces to pads | 5 mil (0.127mm) |
| 3 | Traces width | 4mil (0.1 mm) |
| 4 | With Solder mask dam for SMD to SMD pads | 9 mil (0.23mm) |
| 5 | Without Solder mask dam for SMD to SMD pads | 4 mil (0.1mm) |
| 6 | Traces to outline of Concave cup | 5 mil (0.127mm) |
| 7 | Traces to outline of Bumping | 8 mil (0.2mm) |
| 8 | Traces to Board edge solder mask | 3mil (0.076mm) |
Solder mask & Silkscreen Design Rule
| Sl.No | Item | Min: Rule / Standard |
| 1 | Min PADS Spaces On large copper to keep solder mask dam | 9 mil (0.23mm) |
| 2 | Solder mask openings size | 12 mil (0.3mm) |
| 3 | Solder mask openings for outline, <=1mm finish boards thickness (single side pcb) | 10 mil (0.254mm) |
| 4 | Solder mask openings for outline, >1mm finish boards thickness (single side pcb) | 12 mil (0.3mm) |
| 5 | Min. silkscreen Heigth | 32 mil (0.8mm) |
| 6 | Min. silkscreen Width | 20 mil (0.5mm) |
| 7 | Min. silkscreen Line | 6.4 mil(0.16mm) |
Drilling and its spacing Design Rule
| Sl.No | Item | Min: Rule / Standard |
| 1 | Hole to board edge | Min. 1.5 X (boards thickness) |
| 2 | Punching holes size | Min. 1 X (board thickness) |
| 3 | Min. drilling hole size | Min. 1 X (board thickness) |
| 4 | Solder mask openings to outline opening | 5 mil (0.127mm) |
| 5 | Solder mask openings size for Concave cup | 3 mil (0.076mm) |
| 6 | Solder mask openings for bumping | 2 mil (0.05mm) |
| 7 | Openings R size | 0.5mil (0.127mm) |
| 8 | Outline R size , inner | 0.5mil (0.127mm) |
| 9 | Outline R size, outside | 1.0mil (0.0254mm) |
| 10 | Min. Pedestal to Pedestal | 98.4mil (2.5mm) |
| 11 | Silkscreen to pads size | >6mil (>0.152mm) |
| 12 | Min. Hole edge to outline and V score line | 1.5 T |
| 13 | Min. Thread holes size | >=1T, min. 1.6mm |
| 14 | Min. Rail | 393.7mil (10mm) |
| 15 | Min. Pedestal copper to PADS | 7.87mil (0.2mm) |
Copper Foil Thickness: Normal 1 Oz
Insulation / Dielectric Thickness: Normal 0.1mm (Conductive rate 2w/mk for general FR4)
Copper base thickness: 0.5 / 0.8 / 1.0 / 1.2 / 1.5 / 1.6 / 2.0 (Material C1100)
Min bumping copper size: 2mm (Need evaluate if less than 2mm)
Min bumping to pad size: 0.2mm for 1oz copper
Min FR4 PP: 1.6mm
Min Conductive Dielectric: 2.5mm
For finished 1.5Oz Copper: All of the above parameter need to add 2mil extra
For finished 2Oz Copper: All of the above parameter need to add 4mil extra
