PIN SOCKETS (CAGE JACKS)HAVE MINIMUM PARASITIC RESISTANCE, INDUCTANCE AND CAPACITANCE CONTACTS COPPER --- SOLDER PCB DIELECTRIC ELECTRIC F72 SOLDER SOLDER 一 CAPPED OR UNCAPPED VERSIONS AVAILABLE Figure 9. 4 There is a commercial breadboarding system which has most of the advantages of "birds nest over a ground plane, or deadbug" (robust ground, screening, ease of circuit alteration, low capacitance and low inductance)and several additional advantages: -it is rigid, components are close to the ground plane, and where necessary node capacitances and line impedances can be calculated easily. This system is made by Wainwright Instruments and is available in Europe as"Mini Mount" and in the usa(where the trademark"Mini-Mount" is the property of another company) as"Solder-Mount"[Reference 2 Solder- Mount consists of small pieces of PCB with etched patterns on one side and contact adhesive on the other. They are stuck to the ground plane, and components are soldered to them. They are available in a wide variety of patterns, including ready-made pads for IC packages of all sizes from 8-pin SOICs to 64- pin DILs, strips with solder pads at intervals(which intervals range from 0.040"to 0. 25", the range includes strips with 0. 1" pad spacing which may be used to mount DIL devices), strips with conductors of the correct width to form microstrip transmission lines (50ohms, 60ohms, 75ohms or 100ohms)when mounted on the ground plane, and a tS riety of pads for mounting various other components. A few of the many types of older- Mount building-block components are shown in Figure 9.5
6 PIN SOCKETS (CAGE JACKS) HAVE MINIMUM PARASITIC RESISTANCE, INDUCTANCE AND CAPACITANCE Figure 9.4 There is a commercial breadboarding system which has most of the advantages of "bird's nest over a ground plane, or deadbug" (robust ground, screening, ease of circuit alteration, low capacitance and low inductance) and several additional advantages:- it is rigid, components are close to the ground plane, and where necessary node capacitances and line impedances can be calculated easily. This system is made by Wainwright Instruments and is available in Europe as "MiniMount" and in the USA (where the trademark "Mini-Mount" is the property of another company) as "Solder-Mount"[Reference 2]. Solder-Mount consists of small pieces of PCB with etched patterns on one side and contact adhesive on the other. They are stuck to the ground plane, and components are soldered to them. They are available in a wide variety of patterns, including ready-made pads for IC packages of all sizes from 8-pin SOICs to 64-pin DILs, strips with solder pads at intervals (which intervals range from 0.040" to 0.25", the range includes strips with 0.1" pad spacing which may be used to mount DIL devices), strips with conductors of the correct width to form microstrip transmission lines (50ohms, 60ohms, 75ohms or 100ohms) when mounted on the ground plane, and a variety of pads for mounting various other components. A few of the many types of Solder-Mount building-block components are shown in Figure 9.5
SAMPLES OFSOLDER-MOUNT COMPONENTS I■■■ ■国 〓蠱 器吗suU Figure 9.5 The main advantage of Solder- Mount construction over "bird s nest or"deadbug "is that the resulting circuit is far more rigid, and, if desired, may be made far smaller (the latest Solder- Mounts are for surface-mount devices and allow the construction of breadboards scarcely larger than the final PCb, although it is generally more convenient if the prototype is somewhat larger). Solder- Mount is sufficiently durable that it may be used for small quantity production as well as prototyping Figure 9.6 shows an example of a 2. 5GHz phase-locked-loop prototype built with Solder-Mount. This is a high speed circuit, but the technique is equally suitable for the construction of high resolution low frequency analog circuitry. a particularly convenient feature of Solder- Mount at VhF is the ease with which it is possible t make a transmission line
7 SAMPLES OF "SOLDER-MOUNT" COMPONENTS Figure 9.5 The main advantage of Solder-Mount construction over "bird's nest" or "deadbug" is that the resulting circuit is far more rigid, and, if desired, may be made far smaller (the latest Solder-Mounts are for surface-mount devices and allow the construction of breadboards scarcely larger than the final PCB, although it is generally more convenient if the prototype is somewhat larger). Solder-Mount is sufficiently durable that it may be used for small quantity production as well as prototyping. Figure 9.6 shows an example of a 2.5GHz phase-locked-loop prototype built with Solder-Mount. This is a high speed circuit, but the technique is equally suitable for the construction of high resolution low frequency analog circuitry. A particularly convenient feature of Solder-Mount at VHF is the ease with which it is possible to make a transmission line
SOLDER-MOUNT PROTOTYPE 图 Figure 9.6 If a conductor runs over a ground plane it forms a microstrip transmission line Solder- Mount has strips which form microstrip lines when mounted on a ground plane(they are available with impedances of 50ohms, 60ohms, 75ohms, and 100ohms). These strips may be used as transmission lines, for impedance matching or simply as power buses. Glass fiber/epoxy PCB is somewhat lossy at VhF and UHF, but the losses will probably be tolerable if microstrip runs are short. Both the"deadbug "and the"Solder -Mount"breadboarding techniques become tedious for complex circuits. Larger circuits are often better prototyped using more formal layout techniques An approach to prototyping more complex analog circuits is to actually lay out a double-sided board using CAD techniques. PC-based software layout packages offer ease of layout as well as schematic capture to verify connections. Although most layout software has some amount of auto-routing capability, this feature is best left to digital designs. After the components are placed in their approximate position, the interconnections should be routed manually following good analog layout guidelines. After the layout is complete, the software verifies the connections per the schematic diagram net list Many design engineers find that they can use Cad techniques(reference 3) to lay out simple boards themselves, or work closely with a layout person who has experience in analog circuit boards. The result is a pattern generation tape(or Gerber file)which would normally be sent to a PCb manufacturing facility where the final board is made. Rather than use a pc board manufacturer. however automatic drilling and milling machines are available which accept the PG tas ctly by drilling all holes and using a milling technique to remove copper and create t (Reference ese systems produce single and double-sided circuit boards dir insulation paths and finally, the finished board. The result is a board very similar to the final manufactured double-sided Pc board, the chief exception being that there
8 "SOLDER-MOUNT" PROTOTYPE Figure 9.6 If a conductor runs over a ground plane it forms a microstrip transmission line. Solder-Mount has strips which form microstrip lines when mounted on a ground plane (they are available with impedances of 50ohms, 60ohms, 75ohms, and 100ohms). These strips may be used as transmission lines, for impedance matching, or simply as power buses. (Glass fiber/epoxy PCB is somewhat lossy at VHF and UHF, but the losses will probably be tolerable if microstrip runs are short.) Both the "deadbug" and the "Solder-Mount" breadboarding techniques become tedious for complex circuits. Larger circuits are often better prototyped using more formal layout techniques. An approach to prototyping more complex analog circuits is to actually lay out a double-sided board using CAD techniques. PC-based software layout packages offer ease of layout as well as schematic capture to verify connections. Although most layout software has some amount of auto-routing capability, this feature is best left to digital designs. After the components are placed in their approximate position, the interconnections should be routed manually following good analog layout guidelines. After the layout is complete, the software verifies the connections per the schematic diagram net list. Many design engineers find that they can use CAD techniques (Reference 3) to lay out simple boards themselves, or work closely with a layout person who has experience in analog circuit boards. The result is a pattern-generation tape (or Gerber file) which would normally be sent to a PCB manufacturing facility where the final board is made. Rather than use a PC board manufacturer, however, automatic drilling and milling machines are available which accept the PG tape (Reference 4). These systems produce single and double-sided circuit boards directly by drilling all holes and using a milling technique to remove copper and create insulation paths and finally, the finished board. The result is a board very similar to the final manufactured double-sided PC board, the chief exception being that there
is no"plated-through"hole capability, and any"vias"between the two layers of the mil=0.001")and 12 mil spacing between traces are standard, although smale.s(1 board must be wired and soldered on both sides. minimum trace widths of 25 mi trace widths can be achieved with care The minimum spacing between lines is dictated by the size of the milling bit, typically 10 to 12 mils. exam mple of such a prototype board is shown in Figure 9.7. This is a"daughte board designed to interface an AD9562 Dual Pulse-Width Modulator in a 44- pin PLCC package to a"mother"board. The leads are on 50 mil centers, and the traces are approximately 25 mils wide MILLED PROTOTYPE PC BOARD 9s6 :2: Figure 9.7 Multilayer PC boards do not easily lend themselves to standard prototyping techniques. One side of a double-sided board can be used for ground and the other side for power and signals. Point-to-point wiring can be used for additional runs which would normally be placed on the additional layers provided by a multi-layer board. However, it is difficult to control the impedance of the point-to-point wiring runs, and the high frequency performance of a circuit prototyped in this manner may differ significantly from the final multilayer board
9 is no "plated-through" hole capability, and any "vias" between the two layers of the board must be wired and soldered on both sides. Minimum trace widths of 25 mils (1 mil = 0.001") and 12 mil spacing between traces are standard, although smaller trace widths can be achieved with care. The minimum spacing between lines is dictated by the size of the milling bit, typically 10 to 12 mils. An example of such a prototype board is shown in Figure 9.7. This is a "daughter" board designed to interface an AD9562 Dual Pulse-Width Modulator in a 44-pin PLCC package to a "mother" board. The leads are on 50 mil centers, and the traces are approximately 25 mils wide. "MILLED" PROTOTYPE PC BOARD Figure 9.7 Multilayer PC boards do not easily lend themselves to standard prototyping techniques. One side of a double-sided board can be used for ground and the other side for power and signals. Point-to-point wiring can be used for additional runs which would normally be placed on the additional layers provided by a multi-layer board. However, it is difficult to control the impedance of the point-to-point wiring runs, and the high frequency performance of a circuit prototyped in this manner may differ significantly from the final multilayer board
SUCCESSFUL PROTOTYPING Always use a ground plane for precision or high frequency circuits Minimize parasitic resistance, capacitance, and inductance If sockets are required, use"pin sockets"("cage jacks") Pay equal attention to signal routing, component placement grounding, and decoupling in both the prototy pe and the final design Popular prototy ping techiniques Freehand"deadbug "using point-to-point wiring Solder -Mount Milled Pc board from CAD layout Multilayer boards: Double-sided with additional point-to- point wiring Figure 9.8 EVALUATION BOARDS Manufacturer's evaluation boards provide a convenient way of evaluating high performance ICs without the need for constructing labor-intensive prototype boards Analog Devices provides evaluation boards for almost all new high speed and precision products. The boards are designed with good layout, grounding, and decoupling techniques. They are completely tested, and artwork (including Pg tape is available to customers Because of the popularity of dual precision op amps in 8-pin DIPs, a universal evaluation board has been developed(see Figure 9.9). This board makes extensive use of pin sockets to allow resistors or jumpers to configure the two op amps in just about any conceivable feedback, input/output, and load condition. The inputs and outputs are convenient right-angle bnc connectors. Because of the use of sockets and the less-than- compact layout, this board is not useful for op amps having gain bandwidth products much greater than 10MHz
1 0 SUCCESSFUL PROTOTYPING Always use a ground plane for precision or high frequency circuits Minimize parasitic resistance, capacitance, and inductance If sockets are required, use “pin sockets” (“cage jacks”) Pay equal attention to signal routing, component placement, grounding, and decoupling in both the prototype and the final design Popular prototyping techiniques: Freehand “deadbug” using point-to-point wiring “Solder-Mount” Milled PC board from CAD layout Multilayer boards: Double-sided with additional point-topoint wiring Figure 9.8 EVALUATION BOARDS Manufacturer's evaluation boards provide a convenient way of evaluating highperformance ICs without the need for constructing labor-intensive prototype boards. Analog Devices provides evaluation boards for almost all new high speed and precision products. The boards are designed with good layout, grounding, and decoupling techniques. They are completely tested, and artwork (including PG tape) is available to customers. Because of the popularity of dual precision op amps in 8-pin DIPs, a universal evaluation board has been developed (see Figure 9.9). This board makes extensive use of pin sockets to allow resistors or jumpers to configure the two op amps in just about any conceivable feedback, input/output, and load condition. The inputs and outputs are convenient right-angle BNC connectors. Because of the use of sockets and the less-than-compact layout, this board is not useful for op amps having gainbandwidth products much greater than 10MHz