1s and 2s2p PCB: To route a signal from the interior of a large array to the edge connector, it may be necessary to use a trace on the backside of the PWB. This is acceptable if the total width of traces, both topside and backside, connected to pins of the same row, does not exceed the total specified in paragraph5.3. The trace should be routed directly beneath the topside trace(s) for the balls of the same row until outside the fan-out region. Figure 5 — Nesting of 256 and 352 PGA packages. Figure 6 — Routing outside fan-out layer allowed in low conductivity PCB. High conductivity PCB allows any routing needed on bottom trace layer while the top routing must remain outside the fan-out region. JEDEC Standard No. 51-11Page 75 Trace design (cont’d)5.5 Buried layer layout (2s2p PCB only)The power and ground planes embedded in the board shall be of 35 m (1 oz) copper +0/-20%. They are to be continuous except for via isolation clearance patterns. The power and ground planes shall terminate 1.0 mm from the edges of the PCB, giving overall plane dimensions as listed in table 2. The power and ground planes must not be present in the 9.5 mm edge connector pattern location shown in figure 2.Table 2 — PCB buried plane sizesPCB Size (+/- 0.25 mm) Buried Plane Size101.5 mm x 114.5 mm 99.5 mm x 99.5 mm127.0 mm x 139.5 mm 125.0 mm x 125.0 mm152.5 mm x 165.0 mm 150.5 mm x 150.5 mm5.6 PCB metalization characteristics for 1s and 2s2p PCBsTop and bottom trace metalization on the PCB shall be 70 m (2 oz) finished thickness after final processing (0.070 mm). This is achieved by starting with a 1 oz copper material and plating to 2 oz during PCB through hole plating process. This process specification should be printed on all drawings to ensure proper processing. The thickness of the copper traces shall be verified to +/- 20% after PCB fabrication because thickness variations greater than this can have an excessive influence on the performance of the PCB.5.7 Solder masks for 1s and 2s2p PCBsSolder masking is required. Openings in the solder mask for the plated through holes shall be at least as large as the via pads without allowing them to merge into one another.6 Hand wiring Connection to edge connector: Connection from the through-holes to the edge connector shall be made with 22AWG copper wire or smaller if the connections are not designed as part of the trace pattern.When the board is intended for use in forced air measurement environments, interconnect wiring to the edge connector shall be on the trailing edge of the board with respect to air flow direction and back side of the board with respect to the component placement. Interconnect wiring shall be outside the fan-out area. Figure 7 shows a suggestion for wiring from the leading edge of the test board to the trailing edge before being routed to the edge connector. Connection from the edge connector to the fan-out perimeter and from the fan-out perimeter to the power dissipation structures must be made in a four-point method for force (power) and sense (measure) purposes. Wire diameters for heating force currents may need to be larger to accommodate high power tests and may require more than one edge connector pin. Use table 3 as a guide to determine the required wire diameter [5,6]. JEDEC Standard No. 51-11 Page 86 Hand wiring (cont’d)Table 3 — Wire size current limitsAWG Wire Size UL Current Capacity, (80 ºC), Amperes MIL-W-5088LAmperes30 0.4 N/A28 0.6 N/A26 1.0 N/A24 1.6 N/A22 2.5 5.020 4.0 8.318 6.0 15.416 10.0 19.414 16.0 31.212 26.0 40.0Air Flow Direction