GB2139007A - Multi-layer printed circuit board - Google Patents

Abstract

A six-layer printed circuit card has first, third and sixth layers which are signal carrying layers for interconnecting various components forming a personal computer. The second and fifth layers are both ground plane layers and the fourth layer of the card is a voltage plane. The components on the printed circuit card include eight input/output (I/O) connectors J1 - J8 to which eight other cards controlling various I/O devices can be connected. Seven of the eight I/O connectors are interconnected to a conventional I/O bus. The eighth connector J8 is interconnected to some lines of the I/O bus and to some lines of the signal carrying layers which form an internal bus. <IMAGE>

Description

SPECIFICATION Multilayer printed circuit board This invention relates to a printed circuit board construction and layout and, more particularly, to a six layer printed circuit board in which eight connectors adapted to receiving up to eight additional input/output attachment circuit boards are provided.

Printed circuit boards and multilayer printed circuit boards are well known in the prior art. These boards are used to affix and interconnect electronic components to form electronic circuits. Examples of such circuits are personal computers, such as the IBM Personal Computer. In the IBM Personal Computer, for instance, the base planar board includes a plurality of electronic components including a microprocessor, random access memory, special logic circuits, such as timers and direct memory access (DMA) circuits associated with the microprocessor and other logic components forming circuits. These circuits are all soldered to a printed circuit board and wire lines deposited on the board are positioned to interconnect all of the components to an operating computer system.In the IBM Personal Computer, five input/output (I/O) slots are provided in which up to five other attachment cards can be connected. For instance, the attachment cards may include a diskette card which contains the electronics necessary to operate a diskette in conjunction with the computer found on the base planar board.

In any electronic system utilizing printed circuit boards, the number of components and hence the sophistication of the system, is limited to the space available. By increasing the components, the designer is faced with the difficult task of properly laying out all of the components in a manner in which the printed wires interconnecting each component may be properly placed on the board without intersecting other wires from other components. In order to lay out a printed circuit board containing many components as well as a plurality of connectors such as eight, which are adapted to receiving input/output cards, great skill and technique is required. In particular, all of the connectors must be laid out to contain the appropriate signals of the I/O bus line.

According to the invention, there is provided in a multilayer printed circuit board having printed wires and plated through holes, a portion of which holes are adapted to receiving the pins of electronic components, said wires and holes on said board being for interconnecting components of a computer including a microprocessor, memory means, logic elements and electronic components all interconnected by lines forming an internal bus, said logic elements including driver circuits responsive to signals on selected lines of said internal bus for driving other lines forming an input/output (I/O) bus, characterised by means on said printed circuit board for interconnecting a plurality of input/output connectors, each capable of receiving for connection thereto another printed circuit board, a portion of of said connectors being interconnected solely to said I/O bus lines and a second portion of said connectors being interconnected with some lines of said I/O bus and some lines of said internal bus.

A preferred embodiment of the invention will now be described by way of example with reference to the following Figures, in which; Figure 1 shows the front, or component, side of a six layer printed circuit board; Figure 2 shows one ground plane layer of the printed circuit board; Figure 3 shows the third signal layer of the printed circuit board; Figure 4 shows the voltage plane layer of the printed circuit board; Figure 5 shows the second ground plane layer of the printed circuit board; Figure 6 shows the back, or pin, side of the printed circuit board; and Figure 7shows the same front side of the printed circuit board as shown in Figure 1 with blocks drawn over the board to indicate where various components fit; Referring now to Figures 1 to 6, the six layers of the multi-layer printed circuit board used with an enhanced personal computer are shown.Figure 1 is the top layer onto which the components are inserted and Figure 6 is the bottom layer to which the various pins from the components are soldered. In Figures 1,3 and 6 which are the signal path planes, the dark areas represent copper which is left after having etched away the light or white areas. Figures 2 and 5 which are ground planes and Figure 4 which is a voltage plane are just the opposite in that the dark areas indicate etched away copper and the light area is solid copper.

Referring again to Figure 1 where the dark areas indicate the copper which is remaining after etching, holes through the board are indicated by either dots 20,26 or squares 22,28, and the lines used for interconnecting components are indicated by the thin lines. The dots such as 20 or 26 are shown in different sizes which is determined by the size of the pins on the components to be inserted. No other significance is associated with the different size dots. Generally, the squares 22 and 28 are used to designate which way the components is to be inserted, such that pin 1 of the component is fit into a square space. It should be noted, however, that it is only the plating around a round hole which is square, and not the hole itself. The same is true with respect to the larger holes, such as 26 and 28.The wires interconnecting the various components, such as lines 30 or 32, can be of two sizes depending upon the amount of current which is to be conducted.

For instance, line 30 is a narrow line indicating a small amount of current is to be flowing therethrough. On the other hand, line 32 is larger in width to indicate that a large amount of current, such as a voltage path, will be utilizing that connection. In addition in Figure 1, a pair of ground pads 34 and 36, which have holes (not shown) therethrough are provided. The pads 34 and 36 are for the purpose of providing good connection between the screw securing the board to the machine frame and the ground plane shown in Figures 2 and 5.

There additionally are provided holes 38 through the entire printed circuit board which are not plated through and not interconnected in circuit with the remainder of the board. These are for the purpose of securing the card into the package of the computer. These holes are indicated generally in Figure 1 by a hollow diamond shape.

Referring now to Figure 2, one of the two ground plane layers is shown. As previously indicated, in the ground plane layer the dark areas represent copper which has been etched away and the light areas represents solid copper. Thus, in Figure 2, the ground plane layer is to a large extent a copper layer. Again, the holes are indicated by either dots or squares and it should be noted that the etching away of the plated through hole is greater than the hole itself to avoid electrical contact between the plated through hole and the ground plane layer. Where contact is desired, such as indicated by area 40, lines surrounding the plated through hole may be etched out so long as the etching is not solid. It is necessary for the hole to electrically contact the remainder of the ground plane and the amount of etching shown in Figure 2 is for identification purposes only.Electrically, the hole through the printed circuit board must be conductively coupled to the remainder of the board. It should be noted that the large etched areas such as 42 have a large etched away area so that the holes 38 (shown in Figure 1) for securing the board to the package are not in electrical contact with the remainder of the ground plane. However, in the case of pads 34 and 36 (shown in Figure 1) this is not the case as indicated by areas 44 which are the actual connection of the ground plane to the frame.

In addition to pads 34 and 36, area 46 electrically couples the ground plane to the power supply, area 48 electrically couples the ground plane to the keyboard cable and area 50 electrically couples the ground plane to the keyboard.

Figure 3 is similar to Figure 1 in that it is another signal path plane where the dark areas indicate the copper remaining and the light areas indicate where the copper has been etched away. Again, whether a hole has a round or a square area of copper remaining is for identification purposes and the physical size of the hole or the lead is the same as explained above with respect to Figure 1.

Referring now to Figure 4, the voltage plane is shown. As was the case with the ground plane shown in Figure 2, the white areas indicate the remaining copper and the dark areas indicate the copper areas etched away. Generally, the majority of the white areas shown in Figure 4 is maintained at a voltage of +5 volts which is connected to the power supply through area 52. However, because the processor requires both +5 and -5 volts as well as + 12 and -12 volts, it is necessary to provide the It 1 2 volts, -12 volts and -5 volts to certain areas. This is indicated by the lines such as 54 which define paths cut away from the main part of the voltage plane and can be used to carry one of the other needed voltages. The voltages may also be carried, for instance in line 32 shown in Figure 1, where such is required.For instance, the area defined by lines 54 would be a +12 volt signal which is applied to the various pins as indicated. Note that where such a +12 volt signal path is applied to a pin of a connector such as at 56, the hole is not etched away at this point, thereby providing the + 12 volts to the plated hole and any pin inserted at area 56. Where it is desired to have the +5 volt voltage applied to a particular pin such as at area 58, lines which are not connected are etched away for identification purposes of a hole only. Again, it is necessary that the plated through hole be electrically connected to the voltage plane, so that etching should not be continuous around the hole.

Referring now to Figure 5, the second ground plane is shown which is identical to the first ground plane shown in Figure 2, except for the areas defined by lines 60 and 62. These lines define a voltage path of -5 volts. It was necessary to place this voltage path defined by lines 60 and 62 on this ground plane because of the lack of room on the voltage plane shown in Figure 4. It would be preferable to have placed these lines on Figure 4 for system performance but spacing requirements dictated otherwise.

Referring now to Figure 6, the back side of the printed circuit board is shown. This back side is another signal path plane and, again, the round dots and square dots and the lines whether thick or thin, indicate the remaining copper. Other than the specific interconnections of the lines, Figure 6 is similar to Figure 1.

By utilizing Figures 1 through 6, it is possible to trace out the entire circuit interconnections. For instance, the lines defining the voltage paths 60 and 62 shown in Figure 5 are interconnected by holes 63 and 64 and line 65 shown in Figure 6 so that electrically the lines 60 and 62 are at the same voltage. Line 62 further goes through the plated hole indicated at area 66 in Figures 1,3 and 5. in Figure 3 specifically, it is seen that a copper connection 68 connects hole 66 to another hole 70 to which the voltage is applied to the entire circuit card from the power supply through a pin of connector P2 (to be described hereafter with respect to Figure 7) which is inserted through hole 70.

Referring now to Figure 7, the populated circuit board looking over the signal path plane of Figure 1 is shown. Each of the blocks indicate a circuit component or a space for a circuit component which is used on the populated board. The various blocks have been labeled with a letter and a number to indicate what the component is. Referring to the table set forth below, the various components are indicated.

TABLE C1 5-50 PFTRIM CAPACITOR 50V C2 47PF15VDC C3 10UF16VDC C4 47PF15VDC C5-6 .047UF 1SVDC C7 47PF15VDC C8 .047UF 15VDC C9 47PF15VDC C10-16 10UF16VDC C17-18 .047UF 15VDC C19 .10UFl6VDC C20-27 .047UF 1SVDC C28 10UF 16VDC C29-36 .047UF 1 SVDC C37 10UF16VDC C38-45 .047UF 1SVDC C46 10UF16VDC C47-52 .047UF 1SVDC C53 .0lUF7VDC C54 10UF16VDC C55 .047UF1SVDC C56 l0UFl6VDC C57 047UF15VDC C58 10UF16VDC C59 l0UFl6VDC C60 047UF15VDC C61 10UF16VDC C62 .047UF1SVDC C63 10UF16VDC C64-67 .047UF 15VDC C68 l0UF16VDC J1-J8 62 PIN EDGEBOARD CONNECTOR J9 5 PIN 90 DEGREE CONNECTOR P1 6 PIN POWER CONNECTOR (KEY=4) P2 6 PIN POWER CONNECTOR (KEY=1) P3 4X1 BERG CONNECTOR (KEY=1) R1 510 OHM R2 510 OHM R4 220 OHM R5 180 OHM R6 33 OHM RN1 4.7 KOHM 15RESISTOR/PACK#10% RN2 8.2 KOHM 15RESISTOR/PACK#10% RN3-RN4 30 OHM 8RESiSTOR/PACK/+10% RNS 4.7 KOHM 15RESISTOR/PACK#10% SW1 8 POS DIP SWITCH TD1 DIGITAL TIME DELAY (5 TAPS 100 NSEC MAX) TD2 DIGITAL TIME DELAY(7NSEC) El NO COMPONENT E2 NO COMPONENT E3 NO COMPONENT E4 NO COMPONENT E5 NO COMPONENT TABLE U1 8284A CLOCK DRIVER U2 74LS245 U3 8088 MICROPROCESSOR U4 NO COMPONENT US 74LS373 U6 74LS244 U7 74LS373 U8 8288 BUS CONTROLLER U9 74LS245 U10 74LS670 U11 74LS373 U12 74LS244 U13 74LS243 U14 74LS244 U15 74LS245 U16 74LS244 U17 74LS244 U18 32KX8ROM U19 8KX8 ROM U20 74S280 U21 74LS175 U22 74LS04 U23 74LS27 U24 74LS00 U25 8259A INTERRUPT REQUEST CONTROLLER U26 8253-5 TIMER/CONTROLLER U27 74LS322 U28 8237A-5 DMA CONTROLLER U29 8255A-5 PARALLEL PERIPHERAL INTERFACE U30-38 64KX1 RAM 200NSEC U39 74LS158 U40 74LS158 U41 74LS244 U42 74LS138 U43 74LS138 U44 24510 PROM U45 74LS138 U46-54 64KX1 RAM 200NSEC U55 74S08 U56 74S138 U57 74LS20 U58 74LS32 U59-67 64KX1 BIT RAM 200NSEC (OPTIONAL) U68 7407 U69 74S00 U70 74S74 U71 74LS04 U72 74LS10 U73 74LS74 U74 74LS00 U75-83 64KX1 BIT RAM 200 NSEC (OPTIONAL) U84 NO COMPONENT U85 75477 U86 74LS74 U87 74S08 U88 74LS175 U89 74LS04 XU3 40 PIN DIP SOCKET XU4 40 PIN DIP SOCKET XU18 28 PIN DIP SOCKET XU19 28 PIN DIP SOCKET TABLE XU30-XU38 16 PIN DIP SOCKET XU44 16 PIN DIP SOCKET XU46-54 16 PIN DIP SOCKET XU59-67 16 PIN DIP SOCKET XU75-84 16 PIN DIP SOCKET Y1 CRYSTAL 14.31818 MHZ W1 SOLID AWG 24 WIRE All of the components listed in the table are commercially available components from semiconductor manufacturers such as Intel Corp. of Santa Clara, California or Texas Instruments Corp. of Dallas, Texas.

As noted from the above table, all of the component areas shown in Figure 7 are not necessarily populated. Some, such as U75-U83 are for optional components such as additional memory, while others such as E1-E5 areforfuture expansion. Further, some of the components have a socket between the actual electronic component and the board. For instance, from the chart, it is seen that U3 is an 8088 microprocessor sold by the Intel Corporation. However, noting from the chart, there is also an XU3 component which indicates that a connector is placed between the printed circuit card and the 8088 microprocessor. Such a connector may be any 40 pin dual in-line socket commercially available. In another indication, the component U4 is an extra space as indicated by the lack of a designation for U4.However, the designation XU4 indicates that a 40 pin socket is provided for the insertion of any 40 pin component. For example, an 8087 math processor manufactured by Intel Corporation may be inserted in the space indicated as U4. Further, there are some areas such as El through E5 which do not contain any component or socket.

These are provided for the purpose of allowing the user to reconfigure the board. For instance, if one desired to provide 256K X 1 bit RAM memories in components U30 through U38 or U46 through U54, instead of the 64K as is indicated, it will be necessary to change the component (74LS158) wiring layout in the area indicated by E2 and to add to location U84. Such a chance could be simply shorting a wire and adding a jumper, or soldering in a Berg connector and making an appropriate connection.

In the configuration shown in Figure 7, there are provided either 62 pin edgeboard connectors, into each of which another printed circuit board may be inserted. Such inserted boards may be an attachment card to control a display, a disk or any other I/O or memory attachment card useful with the processor. Attaching such I/O connectors is well known in the prior art such as, for instance, the IBM Personal Computer.

However, in the prior art computer, only five such connectors were provided. By rearranging and reconfiguring the circuit board as is shown in Figures 1 through 6 and populated by the components shown in Figure 7, one is able to add three additional I/O connectors for a total of eight. These additional connectors, and hence the ability to add three additional I/O attachment cards to the computer, greatly increases the usefulness of the computer to its user. By increasing the number of connectors, additional space and lines were required which were not required on the prior art device. To accommodate for the lost space and the additional lines, the signal plane shown in Figure 3 was added, thereby allowing the additional interconnections. This further allowed the components to be physically placed closer together to accommodate the area required for the additional connectors.

Because of long printed wires and high signal frequencies, a problem of electro-magnetic interference may be encountered. To prevent this, a second ground plane is added - as indicated in Figure 2. Thus, the two ground planes shown in Figures 2 and 5 act as a shield between the three signal path planes, in addition to the normal purpose of providing ground connections through the circuit. The second ground plane also provides a better current return to the power supply for logic circuits, thus damping oscillations which could cause electromagnetic radiation.

Referring again to the attachment card connectors J1-J8, it is desirable to connect each pin of each connector identically to the same line of an I/O bus. The 110 bus consists of signal lines generated by the circuits shown in Figure 7 and includes the address bus lines, data bus lines, and the control signals, as well as proper voltage and ground lines. The signals generated by the circuits may be referred to as an internal bus. The required signals are applied through conventional driver circuits to be provided as the I/O bus signals. However, another problem which must be encountered when adding additional connectors is the number of connectors which a driver circuit can drive. This number is based on many things, such as the load of the card placed in each connector. Furthermore, within each card each signal line must be considered. For the layout shown for the printed circuit card shown in Figures 1 through 6, for certain heavily used signals, such as the address and data bus lines, seven is the maximum number of I/O attachment cards which can be driven by the driver circuits. However, because space was made available for the eighth slot, and it was desirable to provide as many I/O connectors as possible, alternate methods of driving the eighth connector are required. This was accomplished by disassociating certain pins of the.eighth connector from the 110 bus which interconnected connectors J1 through J7. For certain pins as can be traced by using Figures 1 through 8, J8 is interconnected to the internal planar I/O bus rather than the I/O bus. For other pins, such as a DMA request or acknowledge signal where very little load is encountered, it is possible and desirable to use the i/O lines themselves. Hence, the interconnection of connector J8 is a hybrid between some lines of the I/O bus and some lines of the planar bus.

For example, it can be seen that at pin 72 in Figure 1, an interrupt signal is provided to connector J8 from the standard I/O bus which interconnects J1 through J7. However, at pin 74 shown in Figure 1 a data line of the 1/09 bus stops. In Figure 6, pin 76 which corresponds to connector J7, pin 74 in connector J8 is connected to lines on the internal bus by line 78. This would be the same signal as is applied to pin 74 in Figure 1 but provided from a different driver circuit.

Claims (4)

1. A multilayer printed circuit board having printed wires and plated through holes, a portion of which holes are adapted to receiving the pins of electronic components, said wires and holes on said board being for interconnecting components of a computer including a microprocessor, memory means, logic elements and electronic components all interconnected by signal lines forming an internal bus, said logic elements including driver circuits responsive to signals on selective lines of said internal bus for driving other lines forming an input/output (I/O) bus, characterised by means on said printed circuit board for interconnecting a plurality of input/output connectors, each capable of receiving for connection thereto another printed circuit board, a portion of said connectors being interconnected solely to said I/O bus lines and a second portion of said connectors being interconnected with some lines of said I/O bus and some lines of said internal bus.

2. A multilayer printed circuit board according to claim 1 wherein said first portion of connectors is greater than said second portion of connectors.

3. A multilayer printed circuit board according to claim 1 or claim 2 wherein said plurality of connectors is eight, said first portion of said connectors is seven and said second portion of connectors is one.

4. A multilayer printed circuit board according to any of claims 1 to 3 wherein said improvement further comprises jumper means adapted to being changed in accordance with different combinations of memory chips to be used.