Datasheet

General Remarks and Construction of the ACULED VHL
The ACULED VHL board is based on an insulated metal core substrate (IMS) made from
copper and a highly sophisticated isolation material with a low thermal resistance between the
copper and chip pads. This package provides excellent heat dissipation and thermal
management from the chip to the substrate’s backside. The thermal resistance R
th JB
of the
entire package is quite low, depending on the chip configuration. To dissipate the heat,
adequate cooling must be considered. To avoid damaging the LED chips by overheating when
equipped with at least one high-power LED chip, the ACULED must not run without appropriate
cooling - even at lower currents.
Figure 1 shows the typical layout of the ACULED VHL. The chips are placed in the middle of the
board, protected by a PPA-based ring and silicone resin encapsulation. The latter is transparent
and suitable for a wide range of radiation from ultraviolet (UV) to infrared (IR). It is also more
resistant to heat than epoxy resin, and its heat expansion characteristics are closer to those of
chips. With the ACULED’s high-power LEDs, silicone achieves superior resistance to light
radiation, mitigating degradation, and maintaining LED color purity over the LED’s lifetime. The
mechanical stress applied to the chips is lowest with silicone, as compared to standard
encapsulation materials. Due to its softness, pressure to the silicone area within the ring must
be avoided. Please refer to the application note “Handling of LED and Sensor Products
Encapsulated by Silicone Resin” to learn more about handling silicone-based products such as the
ACULED.
The clockwise numbered pads C1 - C4 inside the encapsulation ring show the pads where the
LED chips are placed. The distance between the chips is typically 0.2 mm with a pitch of 1.2
mm. Therefore, the lighting area is approximately 2.2 x 2.2 mm², depending on the particular
chip configuration for the specific ACULED VHL or ACULED DYO product. The numbers of the
soldering pads run counter-clockwise from pin 1 to pin 8. The pad numbers 4 and 5 are printed
on the board. Pin 1 is easily located by the small gold dot, which can be used as a reference for
mounting. Whether ESD protection diodes should be used depends on the ESD sensitivity of
the LED chips and is referenced in the specific datasheets of the products.
The tracks on the ACULED are made from copper with a thin gold layer to achieve better
bonding results.
Figure 1
Layout and Dimensions of the
ACULED VHL.
www.excelitas.com Driving the ACULED® VHL™ 3