PCB Tech - PCB design for analysis of laser flash in manufacturing

PCB design for analysis of laser flash in manufacturing
In the process of manufacturing and operation, one of the biggest problems or threats to PCBs is heat. Ironically, heat is an integral part of the manufacturing process, especially during the assembly process where components are soldered to the board. In fact, for surface mount technology, a reflow oven is used, and the circuit board has to withstand a considerable period of time.

Evaluating the temperature that the board will endure is an aspect of good PCB design. It requires an understanding of how the heat is distributed and the board temperature change or thermal diffusivity. This parameter mainly depends on the material of the circuit board and its thickness, and is usually determined by applying laser flash analysis (LFA). After first clearly defining the thermal diffusivity to be determined, let's look at how to make LSA for PCB. Then, we will be ready to propose a way to incorporate this thermal management into the design process.

Understand the thermal diffusivity of PCBA

Unless dealing with high-power PCBs, thermal management is usually not a major consideration, because heat dissipation or heat dissipation is critical on high-power PCBs. This is indeed very important; however, it is only one aspect of good thermal management. In order to get a better and more comprehensive view, it may be helpful to define some terms.

PCB thermal management terms:

Heat dissipation

Heat dissipation is the process of removing excess heat from the circuit board. There are many technologies to achieve this goal. Including the use of high-power components of the radiator and geographically superior heat dissipation holes. Heat dissipation is the main heat dissipation problem during operation.

Heat distribution

For PCB assembly, the temperature of the circuit board must be increased. If lead-free solder is used, these temperatures may be around 250°C (482°F). In contrast to PCB operations (the goal is to remove excess heat as quickly as possible), ensuring the uniform distribution of heat during the manufacturing process is the goal of obtaining high-quality solder joints.

Thermal diffusivity

Unless artificially forced or pumped, heat is always transferred from a higher temperature to a lower temperature. Thermal diffusivity is the rate at which this transfer occurs on the circuit board.

From these definitions, we can see that thermal diffusivity is an important parameter for dissipation during operation and during manufacturing. Now, let's see how to determine this parameter for manufacturing.

Laser flash analysis for PCB manufacturing?

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Laser Flash Analysis (LFA) equipment

In the figure above, an example of a device used to perform LFA is shown. The example in the figure represents a sheet. The test is usually carried out in a closed machine, and the results are analyzed by software. The parameter of interest is the thermal diffusivity, which can be determined using the following formula:

(1) α = K / (⍴c p)

α is the thermal diffusivity

k is the thermal conductivity,

⍴is the material density,

c p is the specific heat capacity.

All variables of the equation. (1) It is related to temperature. This allows determining the change when the temperature rises. With these data, you can achieve accurate thermal analysis for your design, thereby achieving effective thermal management.

Analysis and Design of Laser Flash in PCBA Manufacturing

The results of the LSA can be used to ensure that the selected board material and PCB layout are optimized for your manufacturing process. In addition, Cadence's Celsius Thermal Solver can be used to complete integrated thermal management strategies including electric and thermal co-simulation.

Cadence's PCB design and analysis platform is an advanced comprehensive system design tool that can provide you with integrated design, SI/PI analysis and thermal management. With Allegro, you can optimize your manufacturing design and manufacture circuit boards faster and with the highest quality.