Modular active board subassemblies and printed wiring boards comprising the same

A modular active board subassembly for coupling a waveguide array to an electrical component on a printed wiring board may include a substrate board with a sidewall extending around at least a portion of an attachment surface of the substrate board and forming a component cavity on the attachment surface. A transceiver may be disposed in the component cavity proximate an inboard edge of the substrate board. The transceiver may be electrically coupled to conductors on the attachment surface and electrically coupled to electrical contacts on an upper surface of the sidewall. A waveguide may be positioned in the component cavity and extend from the outboard edge of the substrate to the transceiver. The waveguide may be coupled to the transceiver.

BACKGROUND

The present specification generally relates to active wiring board interconnects and, more specifically, to modular active board subassemblies and printed wiring board assemblies comprising the same.

2. Technical Background

High performance computers require high speed data interconnections between hundreds or even thousands of discrete processing units. In a typical computer system these processors may be deployed on multiple printed wiring boards installed in several different racks. As data rate requirements increase, the growing cost and physical size of electrical interconnection cables has driven system architects to switch to optical links. The trend toward optical interconnects, which started in long- and medium-length rack-to-rack links, is continuing as the demand for high speed data interconnections increases. However, the use of traditional “cables” to bring optical signals directly to processing units is cumbersome and requires the use of connectors on the board surface proximate the processing units which take up valuable space on the mounting surface of the printed wiring board. Further, placement of the optical cables over the surface of the board can interfere with air flow over the board and, as a result, adversely impact the cooling of electronic circuits located on the board. Accordingly, a need exists for alternative optical interconnects.

SUMMARY

A modular active board subassembly for coupling a waveguide array to an electrical component on a printed wiring board may include a substrate board with a sidewall extending around at least a portion of an attachment surface of the substrate board and forming a component cavity on the attachment surface. A transceiver may be disposed in the component cavity proximate an inboard edge of the substrate board. The transceiver may be electrically coupled to conductors on the attachment surface and electrically coupled to electrical contacts on an upper surface of the sidewall. A waveguide may be positioned in the component cavity and extend from the outboard edge of the substrate to the transceiver. The waveguide may be coupled to the transceiver.

In another embodiment, a printed wiring board assembly includes a primary substrate and a modular active board subassembly. The modular active board subassembly may include a substrate board having an attachment surface extending between an inboard edge and an outboard edge. A transceiver may be positioned proximate an inboard edge of the substrate board. At least one waveguide may be positioned on the attachment surface. The waveguide may extend from the outboard edge of the substrate to the transceiver such that the at least one waveguide is coupled to the transceiver. The active board assembly may also include an waveguide connector aligned with the outboard edge. The primary substrate may include a component mounting surface having a plurality of electrical contacts spaced apart from a peripheral edge. A board receiving slot may extend from a peripheral edge of the primary substrate in an inboard direction. The modular active board subassembly may be positioned in the board receiving slot such that the at least one waveguide and the transceiver are recessed from the component mounting surface and an outboard edge of the modular board assembly is aligned with the peripheral edge of the primary substrate.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of printed wiring board assemblies and modular active board subassemblies for incorporation in printed wiring board assemblies, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. One embodiment of a printed wiring board assembly is schematically depicted inFIG. 4. The printed wiring board assembly includes a primary substrate and a modular active board subassembly. The printed wiring board is formed with a board receiving slot which extends from a peripheral edge of the primary substrate inwards. The modular active board subassembly includes at least one waveguide extending between an outboard edge and a transceiver positioned proximate on inboard edge. The modular active board subassembly may be positioned in the board receiving slot of the primary substrate such that the waveguide and transceiver are recessed from the component mounting surface of the primary substrate. Printed wiring board assemblies and modular active board subassemblies for incorporation in printed wiring board assemblies will be described in more detail herein.

Referring now toFIGS. 1-3, a modular active board subassembly100which may be incorporated into a printed wiring board assembly is schematically depicted. In one embodiment, the modular active board subassembly100generally comprises a substrate board102on which a component mounting cavity126is formed. In the embodiments shown and described herein, the substrate board102is formed from commercially available printed wiring board material which may include a lamination of conductive layers alternately arranged with dielectric insulating layers. For example, in one embodiment the printed wiring board may be formed from alternating layers of copper and FR-4 glass fiber/epoxy resin dielectric material. However, it should be understood that other suitable printed wiring board materials may be used to form the substrate board including, without limitation, rigid wiring board materials and flexible wiring board materials.

The substrate board102includes an attachment surface104to which various electrical, opto-electrical and/or optical devices may be mounted. The attachment surface104extends between an outboard edge106and an inboard edge108. The component cavity126is formed on the attachment surface104by one or more sidewalls128extending around at least a portion of the perimeter of the attachment surface104. For example, in one embodiment (not shown) the sidewalls128may extend around the entire perimeter of the attachment surface104. In another embodiment, the sidewalls extend around a portion of the perimeter, as depicted inFIG. 2. In yet another embodiment (not shown) the sidewalls may be formed on the attachment surface104at locations where the opto-electronic components and/or electronic components are located thereby forming component cavities around the opto-electronic and/or electronic components.

In the embodiments shown and described herein the component cavity126is formed on the attachment surface104by positioning a sidewall board120on the attachment surface104. The sidewall board120is a printed wiring board which has been patterned into a “U” shape. The sidewall board120is positioned on the attachment surface104of the substrate board102such that the component cavity126is open at the outboard edge106of the substrate board102. The sidewall board120may be affixed to the substrate board102using epoxies or other similar adhesives and/or bonding agents commonly used in the assembly of electronics.

While the component cavity126has been described herein as being formed by positioning a sidewall board120on the attachment surface104of the substrate board102, it should be understood that, in other embodiments (not shown), the substrate board may be integrally formed with sidewalls128which define the component cavity. For example, in one embodiment (not shown) the substrate board may be formed from discrete patterned layers which, when assembled, form the substrate board including the attachment surface and the sidewalls which define the component cavity.

In one embodiment, the modular active board subassembly100also includes a waveguide connector aligned with the outboard edge106of the substrate board102. The waveguide connector is operable to mate with a corresponding waveguide array connector154, such as the waveguide array connector of an optical cable150. The waveguide connector may include at least one alignment feature for aligning the waveguides of the modular active board subassembly100with waveguides of a waveguide array. For example, the waveguide connector may include dovetails, slots, pins, receptacles or other, similar alignment features. In the embodiment of the modular active board subassembly described herein, the waveguide connector comprises a pair of alignment pin receptacles122for receiving the connector pins156of a waveguide array connector154. In the embodiments described herein the alignment pin receptacles122are located in the sidewall128proximate the outboard edge106of the substrate board102. The alignment pin receptacles122are substantially parallel to the attachment surface104of the substrate board102. However, it should be understood that the modular active board assembly may also be formed without a waveguide connector. For example, when the modular active board assembly is formed without a waveguide connector, waveguides located on the modular active board assembly (described in more detail herein) may be passively or actively proximity coupled to waveguides on a primary substrate or waveguides located on another component.

The active modular board subassembly100also includes a transceiver130. In the embodiments described herein, the transceiver130is operable to convert electromagnetic energy, such as visible light, infrared radiation, microwave energy or the like, to an electronic signal and convert electronic signals to electromagnetic energy which can be guided by a waveguide. More specifically, in the embodiments described herein the transceiver130is an opto-electronic transceiver which is operable to receive an optical input signal and convert the optical input signal into an electrical output signal. The opto-electronic transceiver may also be operable to receive an electrical input signal and convert the electrical input signal into an optical output signal. The transceiver130is positioned in the component cavity126and mounted on the attachment surface104of the substrate board102proximate to the inboard edge108of the substrate board102. In the embodiments shown and described herein, the transceiver130is electrically coupled to electrical conductors112attached to the attachment surface104. For example, the electrical conductors112may include flip chip electrical pads. Alternatively, the electrical conductors may comprise wirebonds to adjacent printed wiring board conductive pads. The electrical conductors112are further coupled to electrical contacts124located on an upper surface129of the sidewall128. For example, in one embodiment, the electrical conductors may be electrically coupled to electrical vias which extend through the sidewall128from the attachment surface104to the upper surface129of the sidewall128.

The sidewalls128of the component cavity126extend from the attachment surface104to a height which is generally greater than the thickness of the transceiver130. Accordingly, it should be understood that the transceiver is located in the space between the plane defined by the attachment surface104of the substrate board102and the plane defined by the upper surface129of the sidewalls128, which planes are generally parallel with one another. In one embodiment, the top surface of the transceiver may be at the same height above the attachment surface104as the upper surface129of the sidewalls128of the component cavity126.

In one embodiment (not shown) one or more transceiver support components may be positioned in the component cavity and electrically coupled to the transceiver. For example, transceiver support components such as laser drivers, amplifiers, signal conditioning units and the like may be electrically coupled to the transceiver through electrical traces formed on the attachment surface of the substrate board. The transceiver support components may also be electrically coupled to electrical contacts located on the upper surface of the sidewalls through electrical vias formed in the sidewalls.

The transceiver130is coupled to at least one waveguide110. For example, in one embodiment, where the transceiver is an opto-electronic transceiver, the transceiver130may be optically coupled to a plurality of waveguides wherein each waveguide is operable to guide an electromagnetic input signal (i.e., light) into the transceiver130and/or guide an electromagnetic output signal (i.e., light) from the transceiver130. The waveguides may comprise any suitable waveguide for guiding a specified wavelength of electromagnetic radiation. For example, the waveguides may be optical waveguides, microwave waveguides, infrared light waveguides or the like. In the embodiments described herein the waveguides are patterned optical waveguides, such as polymer waveguides positioned in the component cavity126and formed on the attachment surface104of the substrate board102or silica or silicon waveguides patterned on glass substrates which are attached to the attachment surface104of the substrate board102. Alternatively, the waveguides110may comprise fiber waveguides, such as glass optical fibers or polymer optical fibers. The fiber waveguides may be bonded to the attachment surface of the printed wiring board or, in the alternative, loose optical fibers may be restrained in an internal channel formed in the substrate board102. In another alternative embodiment, the waveguides may comprise hollow core waveguides or planar array waveguides.

As described hereinabove with respect to the transceiver130, the waveguides110are located in the space between the plane defined by the attachment surface104of the substrate board102and the plane defined by the upper surface129of the sidewalls128. The waveguides110extend from the outboard edge106of the substrate board102to the transceiver130where they are coupled to the transceiver130proximate the inboard edge108. In the embodiments shown and described herein, the waveguides110are positioned at the outboard edge106of the substrate board102in the open end of the “U” shaped sidewalls128. This positioning of the waveguides facilitates directly coupling a waveguide array to the waveguides as will be described in more detail herein. In other embodiments (not shown) the sidewalls128may extend around the entire perimeter of the attachment surface104. In this embodiment the waveguides may extend through the sidewalls to the outboard edge106.

Referring toFIG. 2, in one embodiment, the active modular board subassembly further comprises a cover board140. The cover board140is positioned atop and attached to the upper surface129of the sidewalls128. The cover board140is generally constructed from commercially available printed circuit board material as described hereinabove with respect to the substrate board102. The top surface144of the cover board140includes electrical contacts142which are electrically coupled to the electrical contacts located on the upper surface129of the sidewalls128through electrical vias (not shown) in the cover board140. The electrical contacts142facilitate coupling surface mount electrical components, such as integrated circuit components, located on the top surface144of the cover board140to the transceiver130located in the component cavity126between the cover board140and the attachment surface104of the substrate board102.

In the embodiment of the modular active board subassembly100shown inFIG. 3the cover board140is depicted with electrical contacts located proximate the inboard edge108. However, it should be understood that the cover board140may comprise additional electrical contacts for electrically coupling various other integrated circuit components to the transceiver disposed beneath the cover board140in the component cavity and/or transceiver support components positioned in the component cavity. Further, it should also be understood that the top surface144of the cover board140may also comprise a plurality of electrical traces (not shown) which may subsequently be used to electrically couple and interconnect various integrated circuit components on the top surface144of the cover board140, regardless of whether the integrated circuit components are also coupled to the various components of the modular active board subassembly100.

Referring now toFIGS. 4 and 5, the modular active board subassemblies100described herein may be used in conjunction with primary substrates160to form a printed wiring board assembly200. More specifically, a primary substrate160(i.e., a “mother board” or similarly circuit board comprising various integrated circuits and subassemblies including, without limitation, processors, memory modules and the like) is formed from commercially available printed wiring board material which may include a lamination of conductive layers alternately arranged with dielectric insulating layers. For example, in one embodiment the printed wiring board may be formed from alternating layers of copper and FR-4 glass fiber/epoxy resin dielectric material. However, it should be understood that other suitable printed wiring board materials may be used to form the substrate board including, without limitation, rigid wiring board materials and flexible wiring board materials.

The primary substrate160includes a component mounting surface166which includes a plurality of electrical contacts168to which integrated circuits may be electrically coupled. The primary substrate160may also include a plurality of electrical traces (not shown) which electrically interconnect various electrical contacts168to facilitate electrical interconnections between various integrated circuit components. In the embodiments of the primary substrate160described herein, a plurality of electrical contacts168are offset from a peripheral edge162of the substrate in an inboard direction (i.e., the direction indicated by arrow163inFIG. 4).

The primary substrate160also includes at least one board receiving slot164. The board receiving slot164extends from the peripheral edge162of the primary substrate160in an inboard direction and ends at an inboard stop172. The board receiving slot164is complimentary in size and shape to the active modular board subassembly100such that, when the active modular board subassembly is positioned in the board receiving slot164, the outboard edge106of the active modular board subassembly100is flush with the peripheral edge162and the inboard edge108is in close proximity with the inboard stop (such as when there is a slight gap between the inboard edge108and the inboard stop172) or, alternatively, the inboard edge108is in contact with the inboard stop172.

In one embodiment (not shown) the primary substrate includes one or more metallized planes and/or thermally conductive vias adjacent to the at least one board receiving slot164. The metallized planes or thermally conductive vias may be operable to conduct heat away from an active board assembly positioned in the board receiving slot thereby providing a cooling mechanism for the transceiver and/or other electronic components positioned on the active board assembly.

In the embodiment of the primary substrate160illustrated inFIGS. 4 and 5the component mounting surface166of the primary substrate160includes a cutout over the board receiving slot164. In this embodiment, the depth D of the board receiving slot164is approximately the same as the thickness T of the modular active board subassembly100such that the top surface144of the cover board140is flush with the component mounting surface166of the primary substrate160. In other embodiments the upper surface129of the sidewalls128(or, alternatively, the top surface144of the cover board140) may be flush with, lower than, or higher than an intermediate layer167of the primary substrate160, as will be described in more detail herein.

In the embodiments of the printed wiring board assemblies and modular active board subassemblies shown and described herein, the modular active board subassembly100is depicted as having electrical contacts proximate the inboard edge108while the primary substrate is depicted as having electrical contacts on the component mounting surface166proximate the inboard stop172of the board receiving slot164. However, it should be understood that the electrical contacts need not be located proximate the inboard edge108and the inboard stop172of the board receiving slot164. For example, in the alternative, the electrical contacts may be located on the component mounting surface166of the primary substrate160along the length of the board receiving slot164while the electrical contacts of the modular active board subassembly may be located along the length of the modular active board subassembly.

Referring toFIGS. 4 and 5, the modular active board subassembly100may be positioned in the board receiving slot164of the primary substrate160such that the outboard edge106of the modular active board subassembly100is flush with the peripheral edge of the primary substrate160. This may be accomplished by positioning the modular active board subassembly100in the board receiving slot164such that the inboard edge108is in contact with the inboard stop172. In the embodiment depicted inFIGS. 4 and 5the top surface144of the modular active board subassembly100is disposed in the cutout over the board receiving slot such that the top surface144of the modular active board subassembly100is flush with the component mounting surface166of the primary substrate160. This configuration facilitates mounting a circuit component180, such as an integrated circuit component, on the top surface144of the modular active board subassembly100such that the circuit component180is at least partially disposed over the modular active board subassembly100. Once the modular active board subassembly100is positioned in the board receiving slot164and aligned with the peripheral edge162of the primary substrate160, the modular active board subassembly100may be attached to the primary substrate160with epoxy or another similar adhesive or bonding agent. The circuit component180may be electrically coupled to the electrical contacts168on the component mounting surface166of the primary substrate160and the electrical contacts142on the top surface of the modular active board subassembly100with solder balls182. However, it should be understood that other techniques for electrically coupling the circuit component180to the electrical contacts may also be used.

In an alternative embodiment (not shown) the modular active board subassembly may be inverted in the board receiving slot. For example, in this embodiment, the modular active board subassembly is positioned in the board receiving slot such that the surface of the substrate board opposite the attachment surface is flush with the component mounting surface of the primary substrate and the waveguides and transceiver are positioned in the board receiving slot. In this embodiment, circuit components may be at least partially positioned on the surface of the substrate board opposite the attachment surface. In this embodiment, the substrate board may comprise electrical vias extending through the thickness of the substrate board such that the transceiver may be electrically coupled to circuit components positioned on the surface of the substrate board opposite the attachment surface.

FIG. 6depicts another alternative embodiment of a printed wiring board assembly220which includes a modular active board subassembly100. In this embodiment, the modular active board subassembly100is embedded in the primary substrate160as the primary substrate160is constructed. For example, the primary substrate160may be constructed from alternating layers of conductive material and dielectric material as described above. As the alternating layers are built up, a plurality of the layers may be patterned to form the board receiving slot in the primary substrate160. The modular active board subassembly100may be positioned in the board receiving slot as described above. Thereafter, additional alternating layers of conductive material and dielectric material may be positioned over the modular active board subassembly100thereby embedding the modular active board subassembly beneath the component mounting surface166of the primary substrate160. The electrical contacts124on the upper surface of the sidewall of the modular active board subassembly100may be electrically coupled to the electrical contacts168on the component mounting surface166with electrical vias161formed in the layers of conductive material169and the layers of dielectric material170. Thereafter, a circuit component180may be mounted on the component mounting surface166such that the circuit component180is at least partially disposed over the modular active board subassembly100. Moreover, the circuit component180may be electrically coupled to the active modular board assembly with the electrical contacts168.

Referring toFIGS. 3 and 5by way of example, the active modular board subassembly100may be used to couple the circuit component180positioned on the component mounting surface166of the primary substrate160with an interconnect. For example, when the active modular board subassembly is configured to send and receive optical signals, the active modular board subassembly may be optically coupled to an optical cable150. The optical cable150may include an optical fiber cord158which consists of a plurality of waveguides, specifically optical fibers (not shown), in a protective sheath. The optical fiber cord158may be positioned in a strain relief boot152of a waveguide array connector154where the individual optical fibers are separated and fixed into position for optical coupling to another waveguide and/or opto-electronic device. The waveguide array connector154comprises a plurality of connector pins156which extend from the end of the waveguide array connector and are used to align the waveguide array connector with a corresponding connector or device. For example, in the embodiments of the modular active board subassembly100described herein, the alignment pin receptacles122are operable to receive the connector pins156of a waveguide array connector such that when the connector pins16are received in the alignment pin receptacles122, the waveguides110of the modular active board subassembly100are aligned with and optically coupled to the optical fibers in the waveguide array connector154.

Once the optical cable150is optically coupled to the modular active board subassembly100, optical signals from the optical cable150are guided into the waveguides110located in the component cavity126which, in turn, direct the optical signals inboard (i.e., in the direction indicated by arrow163inFIG. 4) to the transceiver130which is electrically coupled to circuit component180. Accordingly, it should be understood that the modular active board subassembly facilitates propagating an optical signal inboard from the peripheral edge of a primary substrate160and, as such, extends the optical link between components closer to the actual circuit component before converting the signal to an electrical signal. Once the optical input signals are received by the transceiver, the transceiver130converts the optical input signals to electrical output signals and outputs the electrical output signals through the electrical contacts on the upper surface129of the sidewalls128. Alternatively, when the modular active board subassembly100also includes a cover board140, the electrical output signals may be output through the electrical contacts on the top surface144of the cover board140. In either embodiment the electrical output signals may be distributed to one or more integrated circuit components, such as circuit component180which is positioned on and electrically coupled to the electrical contacts142on the top surface144of the cover board140.

Similarly, the transceiver130is also operable to receive an electrical input signal from the electrical contacts142on the top surface144of the cover board140and convert the electrical input signal into an optical output signal. For example, the circuit component180may send an electrical input signal to the transceiver130where the electrical input signal is converted to an optical output signal. The transceiver130directs the optical output signal into the waveguides110where the signal propagates into the waveguide array connector154of the optical cable150which may be used to distribute the optical output signal to various other components.

FIGS. 1-6depict the modular active board subassemblies100as being generally rectangular in shape such that the modular active board subassemblies100(and the corresponding board receiving slots164) generally extend inboard from the peripheral edge in a substantially linear fashion. However, it should be understood that the modular active board subassemblies100may be formed in various other shapes.

Referring toFIGS. 7 and 8, by way of example, a primary substrate160is shown which includes a plurality of board receiving slots164. The board receiving slots164are shaped to receive the modular active board subassemblies100disposed over the primary substrate160as shown inFIG. 7. In this embodiment the modular active board subassemblies100are formed with a 90 degree bend between the outboard edge106and the inboard edge108. This configuration facilitates the use of multiple modular active board subassembly on a primary substrate160by locating the inboard edge108of each modular active board subassemblies at a different area of the substrate. This configuration distributes the location of each integrated circuit (not shown) which will be electrically coupled to the modular active board subassemblies over the component mounting surface166of the primary substrate160. The modular active board subassemblies100may be inserted in the primary substrate160in a similar manner as described above to form the printed wiring board assembly230.

While the modular active board subassemblies100are depicted inFIGS. 7 and 8as having a 90 degree bend between the inboard and outboard edges, it should be understood that the modular active board subassemblies100may take on other configurations. For example, the bend between the inboard and outboard edges may be greater than 90 degrees or less than 90 degrees. Alternatively, the modular active board subassembly may include one or more curves between the inboard edge and the outboard edge, such as when the modular active board subassembly is in the form of an arc or an “S” curve.

Further, the embodiment of the printed wiring board assembly230shown inFIGS. 7 and 8is formed in a similar manner as the printed wiring board assembly shown inFIG. 6, i.e., the modular active board subassembly is positioned in the board receiving slot and additional layers of conductive material and/or dielectric material are added to the primary substrate to imbed the modular active board subassembly in the primary substrate160. However, in the embodiment of the printed wiring board assembly230shown inFIGS. 7 and 8, the modular active board subassemblies100further comprise an extension element190located on the top surface144of each modular active board subassembly100. The extension element190may be formed from printed circuit board material and comprises a plurality of vias (not shown) which extend through the extension element190and couple the electrical contacts on the top surface of the modular active board subassembly with the electrical contacts194positioned on the extension element190. Thereafter, the additional layers of conductive material and dielectric material positioned over the modular active board subassembly are formed with an opening of suitable dimensions for receiving the extension element. In this embodiment, the extension element190is flush with the component mounting surface166of the primary substrate160. Similarly, the electrical contacts194of the extension element190are flush with the electrical contacts182positioned on the component mounting surface of the primary substrate160.

Further, while the embodiments depicted inFIGS. 7 and 8show the modular active board subassemblies100as having an extension element190located on the top surface144, such as when the modular active board subassemblies100are formed with a cover board, it should be understood that in other embodiments the extension element190may be positioned on the upper surface of the sidewall, such as when the modular active board subassemblies are formed without a cover board.

It should now be understood that the present specification discloses modular active board subassemblies which may be positioned in a board receiving channel on a primary substrate to form a printed wiring board assembly. The modular active board subassemblies and printed wiring board assemblies incorporating the same present several advantages. For example, the modular active board subassemblies used to form a printed wiring board assemblies facilitate extending the waveguide interconnection of electrical circuit components inboard from the peripheral edge of the substrate while not occupying additional surface area on the component mounting surface of the primary substrate. This allows for the faster exchange of signals between circuit components on different printed wiring board assemblies while freeing up surface area for additional circuit components on a single printed wiring board assembly.

Further, extending the waveguide interconnections inboard of the peripheral edge of the primary substrate eliminates the use of electrical interconnects which, in turn, mitigates RF interference between electrical interconnects and one potential source of errors in data transmission.

Further, use of modular active board subassemblies allows the modular active board subassembly and, more specifically, the waveguide components of the modular active board subassembly to be assembled and aligned independent of the purely electrical components of the primary substrate. As a result, when the modular active board subassembly is assembled into the primary substrate, precise alignment is not necessary as the waveguide components are pre-aligned and only electrical interconnections between the modular active board subassembly and other circuit components and/or the primary substrate are being made. This reduces the overall precision needed for assembly of the primary substrate.

Moreover, use of modular active board subassemblies facilitates testing each subassembly prior to integrating the subassembly into a printed wiring board assembly thereby reducing the number of quality control tests performed on the finished printed wiring board assemblies and decreasing process waste by reducing the amount of non-compliant printed wiring board assemblies resulting from defective modular active board subassemblies.