Today we going to share the pcb knowledge about the copper thickness unit, which should be usefull for the new PCB designers.
The thickness of 1 oz is about 35 um.
1 oz mean weight of the average copper foil in the area of 1 square foot is 28.35g, which use the the weight of unit area to represent the average thickness of copper thinness.
Conversion methods:
1 square foot = 929.0304 square centimeters,
The copper foil weight divided by the density and the surface area,that is the thickness of copper foil!
The density of Cu = 8.9 kg/dm ^ 3
Copper thickness is T
Tx929.0304 square centimeters x8.9 g/cm3 = 1 oz = 28.35 g/cm2,
T = 0.0034287 cm = 34.287 um
The relation between PCB line width and the current
One, the calculation method is as follows:
First calculate the Track sectional area.Most of the copper foil thickness of the PCB is 35 um (if the copper thickness is not sure,you can ask your cooperated PCB manufacturer).The copper thickness multiplied by the line width is the cross-sectional area.Pay attention to the conversion into square millmeter.Experience value in a current density v is 15 ~ 25 amps/mm2.The experience value multiplied by the sectional area is capacity.
I = KT0.44A0.75
K means the correction coefficient.It takes 0.024 when the copper wire is in the inner layer.And it takes 0.048 when the copper wire is in the outer layer.
T means the maximum temperature rise,and the unit is degrees Celsius (copper melting point is 1060 ℃)
A means cross-sectional area of copper, and the unit is square MIL (not mm , pay attention to square MIL.)
I means allowable maximum current, and the unit is the ampere (amp)
Generally, 10 mil = 0.010 inch = 0.254 ,which can be 1 A.250 mil = 6.35 mm, which can be 8.3 A
Two, the data:
The calculation of PCB current-carrying capacity is always lack of authoritative technology method and formula. Experienced CAD engineers rely on personal experience to make more accurate judgment.But for CAD novice, it meets a difficult problem.
PCB current-carrying capacity depends on the following factors:line width, line thickness (copper foil thickness) , the permissible temperature rise.As everybody knows, the wider PCB line is, the greater the current-carrying capacity is.Assuming that under the same conditions, 10 mil line can withstand the 1 A, then how much current can 50 mil line withstand? Is it 5 A?Naturally the answer is “no”.Please see the following data from the international authoritative institutions :
The unit of line width is Inch ( 1 Inch = 25.4 millimetres ) 1 oz copper = 35 microns thickness, 2 oz. = 70 microns thickness, 1 oz = 0.035 mm, 1 mil = 10∧-3 Inch.
In experiments, the length of wire line causes the line resistance that causes the pressure drop,which has to be considered.Tin in the process is just to increase the current capacity,but it is hard to control the volume of the tin.1 OZ copper and 1 mm width, usually 1-3 A . Specifically see your line length and the requirements for the pressure drop.
The maximum current value should mean the maximum allowable value under the temperature limit.Fusing value is the value of copper melting.Eg. 50 mil 1 oz temperature 1060 degrees (i.e. copper melting point), the current is 22.8 A
Safe current of aluminium wire is 4-5 A per square millimeter
Safe current of copper wire is 5-6 A per square millimeter
The copper wire of maximum current can run 10A with one square millimeter.
The relationship between sectional area of wire and the current
Safety calculation method of copper wire is as below:
The safe current-carrying capacity of copper power wire of 2.5 mm² is 28A
The safe current-carrying capacity of copper power wire of 4 mm² is 35A
The safe current-carrying capacity of copper power wire of 6 mm² is 48A
The safe current-carrying capacity of copper power wire of 10 mm² is 65A
The safe current-carrying capacity of copper power wire of 16 mm² is 91A
The safe current-carrying capacity of copper power wire of 25 mm² is 120A
If it is aluminium wire, wire diameter is 1.5 -2 times of copper wire.
If the current of copper wire is less than 28 A, 10A per every square millimeter is safe .
If the current of copper wire is larger than 120A, 5 A per square millimeter is OK.
The current that can normally go through the sectional area of the wire,has a choice according to the sum of needed current.
The aluminum wire below 10 mm², square millimeter number multiplied by five is ok, if the copper wire,rose up a gear
The copper wire of 2.5 square, is calculated at four square. More than one hundred ,they are all cross-sectional area multiplied by 2.
Under 25 square,multiplied by four,
More than 35 square, multiplied by three
70 and 95 square,multiplied by 2.5
Note: it is only as estimation.It is not very accurate.
In addition ,if the copper wire is less than 6 mm² in indoor electronic wire,it is safy that every square current is not more than 10A.From this perspective,you can choose copper wire of 1.5 square or aluminium wire of 2.5 square.
Within 10 meters,the wire current density of 6A is more appropriate.
10 to 50 meters, 3 A/mm²,
50-200 meters, 2 A/mm²,
More than 500 meters, less than 1 A/mm².
From this point of view, if it is not far away, you can choose copper wire of four square or aluminum wire of 6 square.
If that’s the distance of 150 meters of power supply (it is tall buildings or not),copper wire of four square must be adopted .
The impedance of the wire is proportional to its length, and is inversely proportional to the wire diameter.Please use power with special attention to the wire and wire diameter of the input and output wire.In order to prevent the accidents caused by overheat line because of the too big current.