Printed Circuit Boards with Aluminum Core or Carrier - LeitOn-Alu

LeitOn-ALU - Heat mangement with aluminum printed circuit boards

Heat discharge with help of aluminum core enables higher assembly density, improved run-time, and greater reliability in LED technology and high performance transistor areas. Many questions in this new and scarcely researched area deal with design, calcualation, as well as assembly with aluminum core or bearings. Currently 2layer PCBs with aluminum core are available. For aluminum carrier, we provide 1 to 6 layer Printed Circuit Boards. Below we provide some pointers for development, CAD and mounting of aluminum pressed circuit boards.

1. Heat Discharge Calcuation
2. Design rules for Printed Circuit Boards (PCBs) with aluminum core or carrier
3. Soldering Printed Circuit Boards - PCBs with aluminum core or carriers

Soldering PCBs with aluminum cores /carriers

Solder Wave
Soldering aluminum circuit boards on solder waves requires a slower processing time. Otherwise no modifications to the normal soldering process is necessary. The heated solder enters the assembly unit directly from its underside and immediately connects with the present surface (e.g. immersion tin or HAL lead-free, etc.)

Reflow-Soldering
Depending on the aluminum bearing these parameters may change in the reflow soldering process. Aluminum core PCBs´ biggest advantage becomes a problem here: the ability to effectively discharge heat from hot spots.

In how far the soldering characteristics differ from conventional ones particularly depends in two factors:

1. Aluminum carrier/core thickness
2. Printed Circuit Board - PCB size

Since the peak temperature is limited by the resilience of each component the dwell time between heating up and exceeding the melting point remains the only controlled variable. A complete heating of the aluminum bearing is ensured by maintaing the temperature for a longer time so the top temperature does not flow from the soldered spots-to-be. This dwell time should be longer the:

1. thicker the aluminum carrier/core thickness.
2. larger the PCB

Generally, an additional few seconds will be sufficient. Run-up soldering tests are recommended. However, experience has shown that conventional soldering profiles can achieve good smelting as well.

An example (no general validity):

1. pre-heating: room temperature to 110°C
2. main heating: 110 -140°C very slowly
3. melting zone: 265°C at least 35 seconds, because the aluminium absorbs a lot of heat from the soldering spots.

For the solder paste the following characteristics are recommended:

1. higher active flux
2. viscosity silk print: 400 - 600 Pa*s (400.000 - 600.000 cPs)
3. viscosity moulding print: 800 -1000 Pa*s (400.000 - 1000.000 cPs)
4. viscosity Injection print: 150 - 300 Pa*s (150.000 - 300.000 cPs)
5. metal concentration: 85 – 92%
6. pellet form: circula (better than elliptic)

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