Plane copper

HgBa2Ca iCu 02 +2 (n = 1, 2, 3) EEG tensor at the copper, barium, and mercury sites, by Cu( Zn), Ba( Cs), and Hg ( Au) Mossbauer emission spectroscopy. Comparison with point-charge approximation and Cu NMR data showed that the holes originating from defects are localized primarily in the sublattice of the oxygen lying in the copper plane (for HgBa2Ca2Cu30g, in the plane of the Cu(2) atoms)... 

We should not think that heat is lost only from the copper side. The usual laminate (board material) used for SMT (surface mount technology) applications is epoxy-glass FR4, which is a fairly good conductor of heat. So some of the heat from the side on which the device is mounted does get across to the other side, where it contacts the air and helps reduce the thermal resistance. Therefore, just putting a copper plane on the other side also helps, but only by about 10 to 20%. Note that this opposite copper plane need not even be electrically the same point it could for example just be the usual ground plane. A much greater reduction of thermal resistance (by about 50 to 70%) can be produced if a cluster of small vias (thermal vias) are employed to conduct the heat from the component side to the opposite side of the PCB. 

Figure 22 Some idealized models of oxygen and vacancy ordering in the median copper plane. The new periodicities and oxygen contents are specified. The projected and perspective views along the different chains are drawn.

Fig. 2.19 Cadmium deposits obtained from 1.0 M CdS04 in 0.50 M H2SO4 solution onto a copper plane electrode (a) deposition overpotential 10 mV deposition time 24 min, (b) deposition overpotential 40 mV deposition time 4 min, (c) deposition overpotential 60 mV deposition time 2 min, and (d) deposition overpotential 110 mV deposition time 80 s (Reprinted from Refs. [13, 54] with kind permission from Springer)...

Ideally such a perovskite structure contains 3x3 = 9 oxygen atom sites. It was found, however, that the 123 unit cell contains only 7 oxygen atoms. The vacant oxygen sites are in the plane of Y (oxygen coordination. 8, slightly distorted square prism) and in the basal copper plane (Ba oxygen coordination 10). In this way two different Cu sites result, forming the chains and planes of the 123 structure ... 

Fig. 1.28 Zinc deposits obtained by deposition at 35 mV from 0.1 M zincate solution in 1.0 M KOH solution. Deposition time (a) 7 min and (b) 15 min. The substrate is a copper plane electrode (Reprinted from [76] with permission from the Serbian Chemical Society and [7,75] with permission from Springer.)...

The original external conductor chart was developed in 1956. It was assembled from trace heating test data taken from boards of different materials, different thicknesses, and different copper weights, as well as from boards with and without copper planes.The external charts are nonconservative for thin double-sided boards without copper (power, ground, or thermal) planes. Nonconservative in this context means that the traces are higher in temperature for a given current level than the charts suggest. The temperature differences are discussed later in the chapter. 

Five different charts are presented in this chapter. The first has been arotmd since the beginning of the printed circuit industry and is intended for external traces. The second is for sizing internal traces. The third and fourth are for internal and external traces. These are from more recent studies and are referred to as baseline charts. The fifth is used with the baseline charts to account for the heat spreading and cooling effect when copper planes exist in the board. Even with these charts, there are times when charts alone do not offer enough information and analysis tools must be used to solve current carrying capacity problems. 

The external chart. Fig. 16.1, does not include design margin unless there is at least one internal copper plane in the board, such as a power or ground plane. 

Baseline charts.These are additional charts for sizing conductors and show an example of the effect of variables that impact trace temperature rise when current is applied. (Additional baseline charts can be obtained from Thermal Man, Inc., that take into account FR-4, BT, copper planes, and board thicknesses of 0.038 to 0.059 in.) Further discussion follows regarding the significance of the copper weight or thickness, board material, board thickness, and copper planes ... 

Plane chart for a 1.78 mm thick polyimide PWB.This is a chart that describes the reduction in trace temperature rise as a function of the distance from a single copper plane.This chart is used with the internal and external baseline charts. 

The external trace chart represents a best-fit line through trace temperature data points from boards with different materials (epoxy and phenolic, different board thicknesses (3.175 mm [0.125 in.], 1.587 mm [0.0625 in.], and 0.794 mm [0.0312 in.]), and different copper thicknesses (V2 oz., 1 oz., 2 oz., and 3 oz.), and, most important, from boards with copper planes. Board material, board thickness, copper thickness, and especially the copper planes all have an impact on the temperature rise of the trace. Averaging these variables together skews the results. 

The top curve in Fig. 16.3 includes a variety of data points as described previonsly. In Fig. 16.4, several things can be observed with data points O and L, specifically the influence of board thickness and the influence of a copper plane. O and L are the same size trace in boards that are identical, with one exception The board with trace O has a copper plane on the back of the board. A difference of 3 amps is observed between the two cases for a 10°C rise. 

Data point L represents an external, 1 oz. copper trace on a 0.03 in. thick PWB. A trace on a thin board runs hotter than a thicker board. The trace in the thin board reaches a 10°C rise at a lower current level than the other boards. Data point O also represents an external, 1 oz. copper trace on a 0.794 mm (0.0312 in.) thick PWB, although it has a 1 oz. copper plane on the backside of the board.The trace on the board with the copper plane can have significantly more current before reaching a 10°C rise than the trace on the board withont the plane due to the heat-spreading capabUity of the plane. 

The board does not have internal or external copper planes... 

The IPC external conductor-sizing chart should be used only when at least one copper plane (power or ground) exists in the PWB. 

When sizing traces and taking into acconnt the copper planes in the board (still air), consider the following ... 

The distance from a trace to the plane has a significant effect on the temperature rise of the trace. Multiple factors are involved when sizing traces using charts that take into account the heat spreading due to the presence of copper planes ... 

One factor that has significant impact on the temperature rise of a trace for a given current level and trace size is the influence of copper planes. Whether they are power, ground, or simply thermal planes, the copper planes help spread the heat and lower the temperature rise of what would otherwise be a hot spot. 

Figure 16.9 shows the temperature rise of an internal, 0.010 wide, 1 oz. (0.00135 in.) copper trace (13.5 sq. mil), in a 127 mm (5 in.) wide x 127 mm long x 1.78 mm thick polyimide board, with 1.85 amps. The basehne colnmn represents a trace in a board with no copper planes. The other two colnmns represent the same trace and cnrrent, although now there is a 1 oz. copper plane in the board. The trace is centered in the board and can be above or below the plane. The center colnmn illnstrates the temperature rise if the copper plane is 0.508 mm (0.02 in.)... 

FIGURE 16.9 Copper plane influence on trace temperature. 

Significant margin exists in trace sizing if copper planes exist. 

Trace temperature rise has been characterized with respect to board thickness, copper weight, board material, internal versus external, air versus vacuum, as well as the distance from copper planes. A single copper plane has the most significant impact of aU the variables described in this chapter. Guidehnes for estimating trace temperature rise when a copper plane is present are as follows ... 

The baseline represents the trace temperature rise in a PWB with dielectric only (no internal copper planes). 

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