Temperature Rise of PCB Leads

I read two articles today that I found enlightening and cross-referenced to find some information on the subject, most of which give straightforward data, as shown below:

The unit of line width: Inch

Data source: MIL-STD-275 Printed Wiring for Electronic Equipment

Related Tool: Calculator for PCB Trace Width

After reading the article on Temperature Rise in PCB Trace carefully, I have gained a lot, and now I am picking out the important part to better understand the current-carrying capacity of PCB board wire paths. 

We know that the PCB board on the wire current load capacity is limited, and we generally define the maximum load current that a wire of a certain width and thickness can withstand within the specified wire temperature rise under certain environmental conditions. Here we also need to subdivide them into two types of current, continuous current and instantaneous inrush current (continuous current refers to the continuous flow of current through the wire when the circuit is operating. The inrush current is the overload current that instantaneously flows through the wire in excess of the normal continuous current while the circuit is operating. The two conditions have different effects on the temperature rise of the wire, and we need to consider the actual effects of each in our design. 

We intuitively know that heat generation generally starts from R*I^2, R is and the cross-sectional area of the wire (width and thickness of the product), so we can find that this is a non-linear function, and because the wire in the heat while there are multiple ways to dissipate heat, making the model becomes more complex, so we are given a preliminary model and then use the data to fit.

Fitting with DN data:

The introduction of Dummy variables can increase accuracy:

Data fitting results using IPC:

Significance and other implications considered

If we do not pay attention to the above restrictions, the PCB wires will heat up after passing the current and cause continuous heating. When the temperature rises too high, the bonding force between the wires and the substrate insulation material will be destroyed, and the wires will be warped and cannot be used, so the PCB wires are loaded The amount of current cannot exceed the amount of current that causes the temperature to rise and destroys the bond between the wire and the substrate. Especially for power lines and wires that output large loads, the width and thickness of the PCB wires should be calculated with a certain margin. For power supplies For boards or wires with larger currents, you should choose a wider wire based on the size of the current through the fitting curve above, because excessive temperature rise and long-time work may cause the copper foil of the wire to separate from the substrate, warping or bubbling, And even deform the board.
It is worth noting that the solder mask and conformal coating on the PCB will affect the heat dissipation of the wire. Similarly, the load current capacity of the temperature rise wire will be reduced, so we need to compensate for the wire width after the calculation (heat dissipation) When the condition is not good, the width of the wire should be slightly larger than the width of the wire with good heat dissipation).

Another factor is the spacing of the wires. Small spacing, poor thermal design of the board, and poor heat dissipation conditions of the module will increase the temperature rise of the wire, thereby affecting the effective current carrying capacity of the wire.

In PCB processing, the thickness of the copper layer of the wire will increase when the holes are metalized and patterned. The ability to load current is improved, but the side etches of the wire during etching. The width is reduced and the load current is affected. So in the processing process Strictly control the etching quality. Under the normal conditions of the process, the load current capacity of the wire will not be reduced. It will even be slightly improved. This is because the pattern plating method is used to manufacture the PCB. The thickness of the plating is greater than the amount of side erosion of the wire. The actual cross-sectional area increased.