Patent Description:
Vibration related failures in electronic systems are typically caused by high acceleration levels, high stress levels, and large displacement amplitudes. Typically, in electronic assemblies, printed circuit boards (PCBs) are mounted directly to the housing of the electronic assembly, which saves cost and part count. However, it allows for the direct transmission of vibration energy from the housing to the PCB. High acceleration levels at the PCB are driven by direct transmission of energy levels from the surrounding environment. These levels are then amplified by PCB resonance and transmissibility as well as by unsupported large and/or high mass components. Under such conditions, a <NUM> RMS input can be amplified to <NUM> as a result of PCB resonance for on-engine electronics. Stress levels at the PCB and components increase proportionally with vibration levels. Large displacement amplitudes are directly related to resonance of unsupported PCB spans. Large displacements typically result in higher stress levels at electronic component mountings on the PCB and at locations where the PCB is mounted to the housing.

The transmissibility of a PCB (i.e., the ratio of output acceleration to input acceleration excitation) is generally very high. Typically, the transmissibility is on the order of from <NUM> to <NUM>, indicating that transmissibility is one of the main causes for failure as a result of vibration in component parts mounted on PCBs. <FIG> depicts a conventional PCB assembly <NUM>. As can be seen, two PCBs <NUM> are suspended on a chassis <NUM>. Fasteners <NUM> attach the PCBs <NUM> to standoff mounts <NUM> on the chassis <NUM>. Thus, the PCBs <NUM> are directly attached to the chassis <NUM>, and therefore, vibrations from the engine are directly transmitted to the PCBs <NUM> through the chassis <NUM>.

Various attempts have been made to reduce the transmission of vibrations to PCBs. For instance, some of the prior approaches use potting materials or complicated mechanical assemblies to provide PCB support and/or damping. Potting materials, when used in significant volume or in a volumetrically captive design, create issues with matching coefficients of thermal expansion between materials, resulting in the introduction of mechanical stresses as a result of temperature change. With respect to prior mechanical assemblies, the moving parts tend to wear over time and produce metallic dust that interferes with electronics operation. Other prior approaches include utilizing pads that "float" the PCBs so as to isolate them from housings. These pads can add significant cost to the assembly. Additionally, some prior designs use routings through the PCB in close proximity to sensitive components in order to provide strain relief local to those components.

Generally, prior approaches suffer from one or more of the following disadvantages. Some require hand operated machining for the custom molding of parts to conform to PCB geometry, which is labor intensive, difficult to mass produce, and time consuming. The use of potting materials with high coefficients of thermal expansion can cause issues with PCB assemblies, as discussed above. The use of die-cut or custom foam parts is generally expensive in electronics assemblies. Laminates tend to limit component application to one side of the PCB and/or change industry standard manufacturing processes. Some approaches require non-traditional PCB routings/holes that would be difficult for layout, and mechanical assemblies with moving parts or pre-loaded bonds could fail prior to end-of-life of the product.

Accordingly, a device that reduces or dampens vibrations in PCB assemblies, especially in assemblies mounted in industrial settings, and that does not include the same drawbacks as other prior approaches would be desirable. Embodiments of the present disclosure provide such a vibration dampening device for PCB assemblies. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. <CIT> describes an electromagnetic isolation apparatus for an electronic device such as a portable telephone is provided which includes first and second shield cases and elastic members such as rubber cushions. The first and second shield cases are disposed within a casing of the electronic device to surround at least part of both surfaces of a printed circuit board mounted within the electronic device. The elastic members are interposed between an inner wall of the casing of the electronic device and an outer surface of the first shield case and between the inner wall of the casing and an outer surface of the second shield case to produce elastic
pressures urging the first and second shield cases into conductive engagement with the printed circuit board.

<CIT> discloses further relevant prior art.

An apparatus according to the invention is defined in the appended independent claim <NUM>.

Embodiments of a frame for supporting a printed circuit board (PCB) are provided. The frame can be incorporated into a PCB assembly to reduce the transmission of vibration and mechanical shock from a chassis mount to the PCB. In embodiments, the frame increases the resonant frequency of the PCB(s) in the PCB assembly, reduces the peak shear strain at the PCB(s), and/or reduces peak deflection of the PCB(s). Accordingly, the embodiments of the frame for supporting a PCB are able to reduce the occurrences of random vibration failures in electronic assemblies mounted to substrates that experience industrial-level vibrations. These and other advantages will be recognized by a person having ordinary skill in the art based on the following disclosure. While embodiments may be described in a certain context or for a certain application, a person having ordinary skill in the art will readily appreciate that the described frame for supporting a PCB can be used in other contexts and applications.

<FIG> depicts a PCB assembly <NUM>, including an upper PCB <NUM> and a lower PCB <NUM> mounted to a frame <NUM>. In the embodiment shown, the PCB assembly <NUM> is mounted to a chassis <NUM> via standoff mounts <NUM>. The chassis <NUM> can be attached to or supported on, for instance, the housing of an electrical assembly (not shown), or the chassis <NUM> can be a wall of the housing of the electrical assembly itself. In an application of a disclosed embodiment, the electrical assembly, including the PCB assembly <NUM>, is attached to an engine (not shown) or to a mount (not shown) supporting or mechanically attached to the engine. Additionally, for instance, the electronic assembly could also be part of a valve or actuator assembly mounted at the valve on the inlet, exhaust, cooling, or fuel delivery piping of the engine. Thus, the electrical assembly tends to experience vibrations as a result of engine operation that are transmitted from the engine (e.g., through the mount) to the electrical assembly.

Within the PCB assembly, each PCB <NUM>, <NUM> has an upper surface and a lower surface (with upper and lower being relative to the orientation of the PCBs as depicted in <FIG>). The PCBs <NUM>, <NUM> include a plurality of through holes or vias (not shown) into which electronic components <NUM> can be mounted, soldered, or otherwise attached. Electrical connections between the through holes or vias provide electrical communication between the electronic components <NUM> of the PCBs <NUM>, <NUM>. The electrical connections are typically copper paths created in the layers of the PCBs <NUM>, <NUM>. The copper paths can be layered at different levels of the PCBs <NUM>, <NUM> such that a plurality of different paths can be defined and electrically insulated from each other.

A variety of electronic components <NUM> can be mounted to the PCBs <NUM>, <NUM>, including resistors, potentiometers, capacitors, inductors, crystals/oscillators, transformers, batteries, fuses, diodes, transistors, bridge rectifiers, integrated circuits, etc. Moreover, electrical connections can be made between the upper PCB <NUM> and the lower PCB <NUM>, such as through wires or cables that connect the PCBs <NUM>, <NUM>. As depicted in <FIG>, the electronic components <NUM> can, and typically do, have a variety of different heights relative to one another. Also as depicted in <FIG>, the upper PCB <NUM> includes a plurality of terminals <NUM>, such as spring cage terminals, and discrete wires on its upper surface to provide electrical communication to other PCBs, electrical assemblies, controllers, user interfaces, etc..

As discussed, <FIG> depicts an upper PCB <NUM> and a lower PCB <NUM>, with the frame <NUM> therebetween. The upper surface of the lower PCB <NUM> and the lower surface of the upper PCB <NUM> are directed towards the frame <NUM>. The frame <NUM> includes a generally planar substrate <NUM> having an upper surface <NUM> and a lower surface <NUM>. A plurality of ridges <NUM> extend transversely from both of the upper surface <NUM> and the lower surface <NUM>. However, in other examples not covered by the invention as defined in the appended claims, the ridges <NUM> can extend from only a single surface, i.e., just one of the upper surface <NUM> or lower surface <NUM>. According to the invention, the frame <NUM> is made from an electrically non-conductive material such that the PCB <NUM>, <NUM> can be densely populated with electronic components <NUM> without experiencing electrical interference as a result of including the frame <NUM>. In embodiments, the frame <NUM> is made from a plastic material and more preferably from a glass-filled plastic material. In a specific embodiment, the frame <NUM> is made from glass-filled polyamide. In a more specific embodiment, the frame is made from <NUM>% glass-filled polyamide <NUM>/<NUM>. Additionally, in preferred embodiments, the frame <NUM> is an injection molded piece. Using injection molding enhances the reproducibility of the frame <NUM> because molds can be made for specific frame <NUM> configurations.

Additionally, as shown in <FIG>, the ridges <NUM> can extend a height h from the upper surface <NUM> that is different than the height h' from the lower surface <NUM>; however, in embodiments, the height h can be equal to the height h'. The ridges <NUM> define a plurality of recesses <NUM>. The recesses <NUM> are designed to accommodate the electronic components <NUM> that extend from the upper surface of the lower PCB <NUM> and the lower surface of the upper PCB <NUM>. The shape of the recesses <NUM> defined by the ridges can be the same or different across each surface <NUM>, <NUM> of the frame <NUM>, i.e., the recesses <NUM> can include a variety of rectangular, square, triangular, or other polygonal or arcuate shapes. Generally, the shape and size of a recess <NUM> will be selected based on the shape and size of the component that the recess <NUM> is designed to accommodate.

As shown in <FIG>, the ridges <NUM> extending from the upper surface <NUM> of the substrate <NUM> have the same height h and all the ridges <NUM> extending from the lower surface <NUM> of the substrate <NUM> have the same height h'. However, in other embodiments, the substrate <NUM> can be a tiered structure such that the heights h, h' of the ridges <NUM> can vary across the upper and lower surfaces <NUM>, <NUM>. Generally, because the recesses <NUM> are designed to accommodate electronic components <NUM>, the height h or height h' of the ridges <NUM> will be selected to match the tallest electronic component <NUM> mounted to the surface of the PCB <NUM>, <NUM> facing the frame <NUM>.

The frame <NUM> and the PCBs <NUM>, <NUM> are in close spatial relationship such that a plurality of interfaces are created where the ridges <NUM> approach the PCBs <NUM>, <NUM> and/or where the electrical components <NUM> approach the frame <NUM>. As depicted in <FIG>, the upper surface of the lower PCB <NUM> forms a first interface <NUM> with the peaks of the ridges <NUM> extending from the lower surface <NUM> of the substrate <NUM> of the frame <NUM>. Further, the lower surface of the upper PCB <NUM> forms a second interface <NUM> with the peaks of the ridges <NUM> extending from the upper surface <NUM> of the substrate <NUM> of the frame <NUM>. A third interface <NUM> is formed between the lower surface <NUM> of the substrate <NUM> of the frame <NUM> and the top of an electronic component <NUM> mounted on the upper surface of the lower PCB <NUM>. A fourth interface could also be formed between the upper surface <NUM> of the substrate <NUM> of the frame <NUM> and an electronic component <NUM> mounted on the lower surface of the upper PCB <NUM>, but in the embodiments depicted in the Figures, no electronic component <NUM> is in sufficiently close proximity with the upper surface <NUM> of the substrate <NUM> to form such an interface; nevertheless, a fourth interface could be created depending on the selection of electronic components <NUM> for the upper PCB <NUM> and depending on the height h of the ridges <NUM>.

Because the frame <NUM> and one or more electronic components <NUM> may be in contact (as in the case of the third interface <NUM> or the possible fourth interface), the frame <NUM> is preferably reasonably thermally conductive (e.g., greater than <NUM> W/mK) and can act as a heatsink for electronic components <NUM> with moderate dissipation. In the case of an electronic component <NUM> with intermittent transient thermal spikes, a heat spreader (not shown), such as a copper or aluminum plate, strips, meshes, etc., could be molded into the frame <NUM> to facilitate the transfer of heat away from the electronic component <NUM>.

<FIG> provides a magnified view of the interfaces <NUM>, <NUM>, <NUM>. In embodiments, the interfaces <NUM>, <NUM>, <NUM> are created using an elastomeric material. Preferably, the elastomeric materials are electrically non-conductive such that, especially when used in conjunction with the electrically non-conductive frame <NUM>, the PCBs <NUM>, <NUM> can be densely populated with electronic components <NUM> without the elastomeric material causing electrical interference. In a preferred embodiment, the elastomeric material is room temperature vulcanization (RTV) silicone rubber. In another preferred embodiment, the elastomeric material is thermally conductive gap filler, such as Berquist Liqui-Bond® SA <NUM> (Henkel Electronics Materials, LLC, Chanhassen, MN). The elastomeric material provides a flexible joint between the upper PCB <NUM> and the frame <NUM>, between the frame <NUM> and the lower PCB <NUM>, and between an electronic component <NUM> and the frame <NUM>. Additionally, the use of the elastomeric material to create the interfaces <NUM>, <NUM>, <NUM> allows for more tolerance in manufacturing parts to account for differences in height of the ridges <NUM> of the frame <NUM> and the tallest electrical component <NUM> on the PCBs <NUM>, <NUM>. In an embodiment, the tolerance is up to +/- <NUM>", i.e., the elastomeric material can fill in a gap in the interfaces <NUM>, <NUM>, <NUM> of up to +/- <NUM>". In a preferred embodiment, the tolerance can be up to +/- <NUM>". Preferably the tolerance is kept below +/- <NUM>" to reduce the thermal resistance between the electrical component(s) <NUM> and the frame <NUM>. Also, advantageously, the elastomeric material can be deposited via an automated dispensing system on the ridges <NUM> of the frame <NUM>, on the electronic components <NUM> of the PCBs <NUM>, <NUM>, and/or on the PCBs <NUM>, <NUM> themselves.

In conjunction with the elastomeric material, the PCBs <NUM>, <NUM> and the frame <NUM> can also be held together using a plurality of fasteners <NUM> as shown in <FIG>. As depicted in <FIG>, the fasteners <NUM> are located at each of the four corners of the upper PCB <NUM> and the lower PCB <NUM>. Through holes <NUM> are provided in the corners of the upper and lower PCBs <NUM>, <NUM> such that the fasteners <NUM> can be inserted through the upper and lower PCBs <NUM>, <NUM> into sockets <NUM> provided in the frame <NUM>. The fasteners <NUM> can mate with the sockets <NUM> in a variety of suitable ways, including threaded attachment, frictional engagement, snap-fit, etc. In other embodiments, the fasteners <NUM>, through holes <NUM>, and sockets <NUM> can be provided in a greater or lesser number or at different locations on the PCBs <NUM>, <NUM> and frame <NUM>.

As discussed throughout this disclosure, the PCB assembly <NUM> generally includes the PCBs <NUM>, <NUM> and the frame <NUM>. Once these components are secured together via the elastomeric material and/or fasteners <NUM>, the PCB assembly <NUM> can be mounted to a chassis <NUM> as illustrated in <FIG>. As depicted in <FIG>, the PCB assembly <NUM> is attached to the chassis <NUM> via the frame <NUM>. Specifically, the frame <NUM> has at least one side that includes a flange <NUM>. In the embodiment of <FIG>, the frame <NUM> is rectangular, having four sides, with flanges <NUM> on two opposite sides of the frame <NUM>. The flanges <NUM> are secured to the chassis <NUM> via fasteners <NUM> that engage the standoff mounts <NUM>. The fasteners <NUM> are inserted through one or more openings <NUM> in the flanges <NUM>. In preferred embodiments, the openings <NUM> are provided with reinforcement spans <NUM>. As discussed more fully below, the size, shape, spacing, and thickness of the reinforcement spans <NUM> can vary; as depicted in <FIG>, the reinforcement spans <NUM> are triangular in shape.

As compared with a conventional PCB assembly <NUM> (such as depicted in <FIG>) where the PCBs <NUM> are attached directly to the standoff mounts <NUM> of the chassis <NUM>, the PCB assembly <NUM> of the disclosed embodiments (most clearly depicted in <FIG>) is mounted to the chassis <NUM> via the frame <NUM>. In this way, vibrations from the chassis <NUM> are not transmitted directly to the PCBs <NUM>, <NUM>. As such, the frame <NUM> provides a buffer for vibrations transmitted through the chassis <NUM>. As mentioned above, the reinforcement spans <NUM> can vary in size, shape, spacing, and thickness in order to tune the level of vibrations that transfer from the chassis <NUM> through the frame <NUM>. Also advantageously, the spans <NUM> cab be tuned for a significantly different resonant frequency compared to the resonant frequencies of the PCBs <NUM>, <NUM> so that the energy coming through the mounting spans <NUM> does not couple with the resonant frequencies of the PCBs <NUM>, <NUM>.

Embodiments of the PCB assembly <NUM> disclosed herein provide several advantageous properties over conventional PCB assemblies, such as PCB assembly <NUM> shown in <FIG>. For instance, a PCB <NUM> in a conventional PCB assembly <NUM> has a resonant frequency of approximately <NUM> to <NUM>. The PCB assembly <NUM> as depicted, e.g., in <FIG> increases the resonant frequency of the PCBs <NUM>, <NUM> by at least <NUM>%. In particular embodiments, the PCB assembly <NUM> increases the resonant frequency by at least <NUM>%, and in certain embodiments, the PCB assembly <NUM> increases the resonant frequency by as much as <NUM>%.

Embodiments of the PCB assembly <NUM> as depicted, e.g., in <FIG> also reduce the peak shear strain at the PCBs <NUM>, <NUM>. PCB shear strains are on the order of <NUM> in/in for a typical industrial application. The PCB assembly <NUM> can reduce the peak shear strain at the PCB by at least <NUM>% and, in some cases, by as much as <NUM>%. Moreover, the frame <NUM> has the potential to provide more pockets of low strain over the areas of the PCBs <NUM>, <NUM>. Strain levels at the PCBs <NUM>, <NUM> in operation can limit the placement of sensitive components and impact the efficiency and/or the density of the layout, driving larger PCB footprints. Thus, lowering the strain levels provides more options for the placement of sensitive components as compared to conventional PCB assemblies <NUM> (<FIG>), while also maintaining usable board space for placement of electronic components <NUM>. Accordingly, the flexibility of electronic component <NUM> layout is enhanced while the footprint, or size, of the PCBs <NUM>, <NUM> can be reduced.

The PCB assembly <NUM> of, e.g., <FIG> also reduces the peak deflections of the PCBs <NUM>, <NUM>. In a typical industrial setting under typical random industrial vibration levels, a conventional PCB assembly, such as PCB assembly <NUM> (<FIG>), will experience peak deflections of approximately <NUM>". In the embodiments of the PCB assembly <NUM> as shown, e.g., in <FIG>, the frame <NUM> can reduce peak deflection by at least <NUM>% (i.e., a peak deflection of <NUM>") and, in some cases, by as much as <NUM>% (i.e., a peak deflection of less than <NUM>").

In another embodiment of the frame <NUM>' illustrated in <FIG>, a cooling channel (represented by dashed line <NUM>) is provided through one or more of the ridges <NUM>'. In this way, fluid communication is provided between the recesses <NUM>' defined by the ridges <NUM>'. As shown in <FIG>, only a single cooling channel <NUM> is provided across one surface of the frame <NUM>'; however, additional cooling channels <NUM> could be provided across the same surface in a multitude of directions and connecting a multitude of recesses <NUM>'. Moreover, cooling channels <NUM> could also be provided across the opposite surface of the frame <NUM>'. As such, a coolant, such as air, can flow through the frame <NUM>' so as to cool electronic components (not shown) accommodated within the recesses <NUM>'. Further, the cooling channel <NUM> could be filled with a tube or conduit (not shown) containing a cooling fluid, such that, as the cooling fluid flows through the tube or conduit, the cooling fluid thermally conducts heat out of the recesses <NUM>'. Thus, this embodiment of the frame <NUM>' provides many of the same vibration dampening advantages of the previous embodiments while also providing the additional advantage of cooling electronic components contained within the recesses <NUM>' of the frame <NUM>'.

Claim 1:
A frame (<NUM>) for dampening vibrations in a printed circuit board assembly, the frame comprising:
a substrate (<NUM>) having a first surface (<NUM>, <NUM>) and a second surface (<NUM>, <NUM>), wherein the substrate is planar or wherein the substrate is a tiered structure; and
a plurality of ridges (<NUM>) extending transversely from each of the first and second surfaces, the plurality of ridges defining recesses (<NUM>) on each side of the generally planar substrate (<NUM>) and the plurality of ridges on each side configured to mount to a respective printed circuit board (<NUM>, <NUM>);
wherein at least one of the one or more recesses is configured to accommodate one or more electronic components (<NUM>) of the respective printed circuit board in the printed circuit board assembly,
wherein the frame is made from an electrically non-conductive material.