Mounting electronics and monitoring strain of electronics

A system for mounting electronics is disclosed. The system may include a tool and a chassis having a mounting surface. The system may also include an electronics assembly coupled to the chassis. A low modulus spacer may be coupled to the chassis between the mounting surface of the chassis and the electronics assembly. A fastener may couple the electronics assembly and the low modulus spacer to the chassis.

FIELD OF THE INVENTION

Some embodiments described herein generally relate to systems and apparatuses for mounting electronics. Additional embodiments generally relate to methods of attenuating strain transfer and monitoring strain in electronics.

BACKGROUND INFORMATION

In the drilling of oil and gas wells, particularly in directional drilling, the drill string may be subjected to bending as the wellbore is drilled. The drill string rotates during drilling operations and when a portion of the drill string encounters a bend in the borehole, that portion of the drill string may be subjected to increased fatigue loads and cycles as the drill string rotates within the bend. Increased fatigue loads, in the form of strain can lead to premature failure of the drill string.

Printed circuit boards and electronic components may be coupled to the chassis of a drill string. Fatigue loads imparted on the printed circuit boards and electronic components coupled to the printed circuit boards, particularly fatigue loads in the form of strain transferred from the drill string chassis to the printed circuit boards, can reduce the life of the printed circuit boards.

SUMMARY

A system for mounting electronics is disclosed. In one non-limiting embodiment, the system includes a tool and a chassis having a mounting surface. The system also includes an electronics assembly coupled to the chassis. A low modulus spacer may be coupled to the chassis between the mounting surface of the chassis and the electronics assembly. A fastener may couple the electronics assembly and the low modulus spacer to the chassis.

A non-limiting method of mounting electronics is disclosed. The method includes mounting a low modulus spacer onto a surface of a chassis of a tool. The low modulus spacer may include opposing first and second surfaces. The first surface of the spacer may be in contact with the surface of the chassis. The method also includes mounting an electronics assembly to the low modulus spacer. The electronics assembly includes opposing third and fourth surfaces. The third surface of the assembly is in contact with the second surface of the low modulus spacer. The method includes coupling the electronics assembly and the low modulus spacer to the chassis with a fastener.

DETAILED DESCRIPTION

FIG. 1depicts a tool100that includes an electronics assembly140coupled to a tool chassis102. The tool100may be, for example, a downhole tool such as a measurement while drilling tool, a logging while drilling tool, a rotary steerable system, or other type of downhole tool. The electronics assembly140may include a circuit board145, such as a printed circuit board, with electronic components150.

The electronic components150may be active, such as processors, memory, and integrated logic chips, or they may be passive, such as resistors, inductors, and capacitors. The electronic components150may also be other controller hardware, communication hardware, or other electronic components or devices. The electronic components150may be coupled to the circuit board145of the electronic assembly140. In some embodiments, the electronic components150include leads that are soldered to through holes or pads on the printed circuit board145. The solder that couples the electronic components150to the electronic assembly140may form both an electrical and a physical connection to the printed circuit board145.

The electronic assembly140is coupled to the chassis102of the tool100. The electronic assembly140may be coupled to the chassis102of the tool100using a combination of a frame160, a low modulus spacer120, and fasteners190. The fasteners190clamp or otherwise couple the frame160, electronics assembly140, and low modulus spacer120to an outer surface108of the chassis102.

FIG. 2depicts a detailed view of one of the fasteners190and the structure and arrangement of the components that couple the electronics assembly140to the chassis102of the tool100. Each of the frame160, the electronics assembly140, the low modulus spacer120, and the chassis102includes apertures122,142,162,187that form a fastening aperture180.

The chassis aperture187is a blind aperture with threads188that receive and engage with threads198of the fastener190. In some embodiments the chassis aperture187may be a through aperture.

The chassis aperture187has a diameter183that may be the major or outer diameter of the threads188. In some embodiments, the diameter183may be the same as the diameter of a shank196of the fastener190.

The fastening aperture180may also include a clearance portion184. The clearance portion184may include the aperture122in the low modulus material120, the aperture142in the circuit board145of the electronics assembly140, and the aperture162in the frame160. The individual apertures122,142,162may have a diameter185that is greater than the diameter of the shank196of the fastener190. This arrangement provides the clearance portion184of the aperture180with a diameter that is greater than the diameter of the shank196of the fastener190.

In the embodiment shown inFIG. 2, the shank196is the portion of the fastener that passes through the clearance aperture of the assembled tool100. In the embodiment ofFIG. 2, the diameter of the clearance aperture184is greater than the diameter of the portion of the fastener that passes through the clearance portion184of the aperture180that includes the aperture122in the low modulus material spacer120, the aperture142in the electronics assembly140, and an aperture166of the frame160.

The diameter185of the aperture180and the diameter of the portion of the fastener190that passes through the clearance diameter184may be sized such that there is a gap189between the outer surface of the shank196and the inner surface or surfaces of the clearance aperture184. The gap189aids in reducing or preventing contact between the fastener190, the frame160, electronics assembly140, and the low modulus material120. In particular, the gap189aids in reducing or preventing such contact when the chassis102is bent, as discussed later with respect toFIGS. 3 and 4.

The fastener190engages with the frame160and the chassis102to clamp the frame160, electronics assembly140, and the low modulus material120to the chassis102. The threads198of the fastener190engage with the threads188of the chassis aperture187and a head192of the fastener190engages with the shoulder162of the frame160to clamp the frame160, electronics assembly140, and the low modulus material120to the chassis102.

As shown inFIG. 2, a surface168of the frame160contacts an upper surface146of the electronics assembly140. An opposing, lower surface144of the electronics assembly140contacts an upper surface124of the low modulus spacer120and an opposing, lower surface126of the low modulus spacer120contacts the outer surface108of the chassis102. The clamping force between the fastener190and the chassis102is imparted by one surface108,124,126,144,146,166, onto an adjacent surface108,124,126,144,146,166to clamp the low modulus spacer120, the electronics assembly140, and the frame160to the chassis102.

With a low modulus interface material, such as the low modulus spacer120, inserted between electronics module140and the chassis102, the tensile or compressive strain transmitted from the chassis102to the electronics printed circuit board145of the electronics assembly140and components150during bending may be attenuated. The strain from the high elastic modulus chassis102, which may be made from durable materials such as steel, coupled to the low modulus material space120results in much lower relative stresses in the electronics module140as compared to the stress in the chassis102, despite the electronics module140being further from the neutral axis106of the chassis102.

FIGS. 3 and 4depict the tool100in bending. Such bending may occur, for example, when the tool100is passing through a bend or dog leg in a wellbore. Equation 1 depicts the formula for determining the bending stress, σ1, in the chassis102, where E1is elastic modulus of chassis material, c is the distance to the chassis surface108from a neutral axis106, and r is the radius of curvature from the bend or dog-leg.
σ1=(E1*c)/r(Equation 1)

Where ϵ1is the strain, the equation is simplified, as shown in Equation 2.
σ1=E1*ϵ1(Equation 2)

Where E2is elastic modulus of low modulus spacer120and ϵ2is the strain, the stress, σ2, at the lower surface126of the low modulus spacer120that is in contact with the surface108of the chassis102, is shown in Equation 3.
σ2=E2*ϵ2(Equation 3)

Since the strain is the same at surface108of the chassis102and the lower surface124of the low modulus spacer120, because they are at the same distance from the neutral axis106, ϵ1is equal to ϵ2. By combining Equation 2 with Equation 3 and assuming ϵ1is equal to ϵ2, Equation 4 is formed.
σ1/σ2=E1/E2(Equation 4)

By solving Equation 4 for σ2, the stress at a lower surface126of the low modulus spacer120, Equation 5 is formed.
σ2=σ1(E1/E2)  (Equation 5)

Equation 5 may be used to determine the stress at a lower surface126of the low modulus spacer120.

Using Equation 5 and assuming there is no interference between the fastener and the aperture140of the electronics module140, the stress σ3at the surface124of the low modulus spacer120and the surface144of the printed circuit board145of the electronics module140is approximately σ2, the stress at the interface between the low modulus spacer120and the surface108of the chassis102. This assumption works with materials like elastomers, polymers, composites, etc., that exhibit large displacement or strain with little increase in stress or load as compared to metallic alloys. For this approximation, σ2, the stress at the lower surface124of the low modulus material120is assumed to be approximately equal to σ3, the stress at the interface between the upper surface126of the low modulus spacer120and the lower surface144of the circuit board145of the electronics assembly140.

Based on Equation 5 and the assumptions discussed above, the stress at the upper surface126of the low modulus spacer120,63is equal to the ratio of the modulus, E1, of the chassis102and the modulus, E2, of the low modulus spacer120.

As shown below in Equation 6, the tensile stress in the circuit board145of the electronics module140may be expected to have about, for example, approximately 1/10 the stress in the chassis, σ1, when a low modulus spacer120with 1/10 of the elastic modulus of the chassis102is used.
σ3=σ1/10  (Equation 6)

In this embodiment, the strain at the interface between the low modulus spacer120and printed circuit board145may also be the same, as shown in Equation 7.
ϵ3=ϵ1/10  (Equation 7)

Testing with strain gages has shown that actual results are in line with this approximation. Typical data points with elastomer-based low modulus interfaces with ϵ1=150×10−6at the chassis results in strain within a range of ϵ3=15×10−6to ϵ3=30×10−6at the printed circuit board.

As discussed above, the aperture142of the printed circuit board145is greater than the diameter183of the shank196of the fastener190. In addition, the gap189between the fastener190and the inner surface of the aperture142of the circuit board140is such that even under bending during drilling operations, the fastener190may not contact the sidewall of the aperture142. Should one or more fasteners190contact the sidewall of the aperture142, the fastener190may impart a force onto the printed circuit board145and induce stress into the printed circuit board145. Such contact may obviate the strain attenuation that would otherwise be gained by using the low modulus spacer120between the chassis102and the circuit board145of the electronics module140.

Additionally, strain gages could be incorporated on the printed circuit board to aid in monitoring the accumulated strain and fatigue during the operational life of the circuit board145and/or electronic assembly140.

As mentioned earlier,FIGS. 3 and 4depict the tool100in different bending positions. These positions may depict different orientations of the tool100in a well bore. For example, during drilling operations the tool100may rotate within the well bore. When the tool100is located in a bend in the well bore, the tool may be subjected to cyclical bending loads. For example, the rotational displacement of the tool100inFIG. 4is 180 degrees from the tool100, as shown inFIG. 3. During operation, as the tool100rotates within the well bore, the upper surface108of the chassis102, and thus the electronic components150and the circuit board145of the electronic assembly140, may be subject to alternating tensile loads in the orientation shown inFIG. 3and compression loads in the orientation shown inFIG. 4.

These alternating loads cause stress and strain on the electronic assembly140and, in particular, on the electrical traces in the circuit board145and the joints between the electronic components150and the circuit board145. These alternating loads may fatigue the traces and joints which may lead to premature failure of the electronic assembly.

The lower the magnitude of the stress and strain in the electronic assembly140, the longer the electronic assembly will last. Attenuating the strain on the electronic assembly with the low modulus spacer120attenuates the magnitude of the stress and strain imparted to the electronic assembly140by the chassis102.

In some embodiments, materials for use in the low modulus spacer120may also be resistant to or exhibit little to no creep. Creep is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses.

The low modulus spacer120and the distributing component194may be made from low modulus materials such as, for example, delrin, polyamides, lexan, nylon, silicone composites, synthetic rubbers such as fluoroelastomers, nitrile, and viton. In some embodiments the low modulus material may be a composite material including or more low modulus material such as, for example, delrin, polyamides, lexan, nylon, silicone composites, synthetic rubbers such as fluoroelastomers, nitrile, and viton. In some embodiments the composite material may include reinforcing material, such as, for example, fibers or other material.

FIGS. 5 and 6show an embodiment of an electronics assembly240mounted to a chassis202for a tool200. The tool200is a measurement subassembly of a downhole tool and may be used for measuring the properties of the well bore or formations surrounding the tool200. The electronics assembly240may include electronic components250coupled to a circuit board245.

As discussed above with reference toFIGS. 1 and 2, the electronic components250may be active, such as processors, memory, and integrated logic chips, or they may be passive, such as resistors, inductors, and capacitors. The electronic components250may also be other controller hardware, communication hardware, and other electronic components or devices. The electronic components250may be coupled to the circuit board245of the electronic assembly240.

The electronic assembly240also includes a strain gage251mounted to the circuit board245. The strain gage251, along with some of the associated electronic components250may monitor, process, and/or record the strain and fatigue experienced by the electronic assembly240, the circuit board245, and/or electronic components250during operation of the tool200.

In some embodiments, the electronic components250include leads that are soldered to through holes or pads on the circuit board245. The solder that couples the electronic components250to the electronic assembly240may form both an electric and a physical connection to the circuit board245.

The electronic assembly240is coupled to the chassis202of the tool200within a recess209. In some embodiments, an upper surface269of a frame260may be flush with, or radially inward from, an outer surface207of the tool chassis202. In some embodiments, an upper surface252of the electronic components150may be flush with, or radially inward from, the outer surface207of the tool chassis202.

The electronic assembly240is coupled to the chassis202of the tool200using a combination of a frame260, a low modulus spacer220, and fasteners290. The fasteners290clamp or otherwise couple the frame260, electronics assembly240, and low modulus spacer220to an outer surface208of the chassis202.

FIG. 5also shows power and electrical communication wires204for coupling the electronic components250to power and various other subsystems within the tool200and outside the tool200, for example to recording and monitoring equipment located at the surface or another portion of the down hole tool.

FIG. 6depicts a cross-sectional view of the tool200inFIG. 5. As shown inFIG. 6, the fastener290passes through the aperture280and engages with the frame260and the chassis202to clamp the frame260, electronics assembly240, and the low modulus material220to the chassis202. As also shown inFIG. 6, a surface268of the frame260contacts an upper surface246of the electronics assembly240. An opposing, lower surface244of the electronics assembly240contacts an upper surface224of the low modulus material220and an opposing, lower surface226of the low modulus material220contacts the outer surface208of the chassis202. The clamping force between the fastener290and the chassis202is imparted by one surface208,224,226,244,246,268, onto an adjacent surface208,224,226,244,246,268.

FIG. 6also shows a fluid path205within the chassis202of the tool200that provides a path for the flow of drilling fluid or mud.

With a low modulus material interface, such as the low modulus material spacer220, inserted between electronics and chassis, the tensile strain transmitted from the chassis202to the electronics printed circuit board245of the electronics assembly240and components250during bending may be attenuated. The strain from the high elastic modulus chassis202, which may be made from durable materials such as steel, coupled to the low modulus material spacer results in much lower relative stresses in the electronics module140as compared to the stress in the chassis202.

The low modulus spacers120,220may also attenuate the shock amplitude transmitted from the chassis102,202to the electronic assembly140,240, and the electronic components150,250. In combination with the strain attenuation, this may aid providing high reliability and long fatigue life.

A few example embodiments have been described in detail above; however, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the scope of the present disclosure or the appended claims. Accordingly, such modifications are intended to be included in the scope of this disclosure. Likewise, while the disclosure herein contains many specifics, these specifics should not be construed as limiting the scope of the disclosure or of any of the appended claims, but merely as providing information pertinent to one or more specific embodiments that may fall within the scope of the disclosure and the appended claims. Any described features from the various embodiments disclosed may be employed in combination. In addition, other embodiments of the present disclosure may also be devised which lie within the scope of the disclosure and the appended claims. Additions, deletions and modifications to the embodiments that fall within the meaning and scopes of the claims are to be embraced by the claims.

Certain embodiments and features may have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges including the combination of any two values, e.g., the combination of any lower value with any upper value, the combination of any two lower values, or the combination of any two upper values are contemplated. Certain lower limits, upper limits and ranges may appear in one or more claims below. Numerical values are “about” or “approximately” the indicated value, and take into account experimental error, tolerances in manufacturing or operational processes, and other variations that would be expected by a person having ordinary skill in the art.