Page 40 - RSE - Results of the Apollon Project

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Receivers with integrated SOE

In a PV concentration system, the sun power not transformed into electrical power appears as heat. Under high
luminous fux, this heat must be removed as effectively as possible to keep the cell temperature from becoming too
high . Under APOLLON, an extensive research has been carried out on receivers and testing procedures to guarantee
the reliability of this fundamental component.

COB receivers (CRP)

Substrate Selection

The selection of the receiver substrate plays a fundamental role in the reliability of the whole CPV module.
The solar receiver is mainly composed of a substrate onto which one or more solar cells are assembled, a bypass
diode and connectors. The substrate is a crucial choice that affects the performances of the device, thus different
materials are available and both electrical and thermal properties were taken into consideration in the course of
the APOLLON project. Solar receivers require high thermal conductivity materials, so ordinary electronic substrates
such as glass-reinforced epoxy laminate (FR4) are not suitable; high thermal conductivity materials can be divided
into four main categories.

1. IMS (INSULATED METAL SUBSTRATE)
An Insulated Metal Substrate is basically copper FiguRE 37. IMS multistrate
circuitry bonded onto an electrically insulated
dielectric layer, that is in turn bonded to a metallic
substrate, as shown in Figure 37.
The insulating layer plays the key role in the thermal
properties of the IMS, indeed its thermal conductivity
ranges from 1.3 W/mK to 3 W/mK, where the latter is
found in premium quality IMS.

2. THICK FILM ON CERAMIC SUBSTRATES
Ceramic substrates have the advantage of being good electrical insulators with good thermal properties. They
are extremely resistant to high temperatures. The conductive traces are screen printed using thick flm technology.
There are mainly two different ceramic substrates commercially available:
1. Alumina (Al O );
2 3
2. Aluminium Nitride (AlN).

3. DIRECT BONDED COPPER (DBC)
The direct bonded copper substrate is another high FiguRE 38. DBC substrate layers
thermal dissipation substrate for electronics, based on
ceramic insulator.
The copper foils can form an eutectic alloy with the
ceramic substrate, which can still be either alumina or
aluminum nitride. The substrate layers are shown in
Figure 38.
The copper layers can either be pre-formed and
attached to the substrate or attached in their plain

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