SPRING FOR FIXATION AND GROUNDING CONTACT OF A PRINTED CIRCUIT BOARD

Technical field

[0001] The present disclosure relates to a spring for fixation and grounding contact of a printed circuit board (PCB) in a chassis (housing) for electronic components.

Background Art

[0002] Screws have been used as the method to fixate various pieces together, being the PCB in the auto radio's chassis the example to be explored and detailed in this document. Nowadays most electronic devices have a large number of screws, due to the existence of many parts to be assembled under high forces, so it's guaranteed the correct functioning of it during its life time. The electronics devices like auto radios are submitted to a large number of tests before it goes on the market, and one of the most critical is to guarantee the non-displacement of the chassis when submitted to high forces, as a crash.

[0003] Regarding electronic devices the usage of screws is very important, as screws ensure the fastening of several parts or components as well as the electric grounding. This issue is solved by using a large number of screws, which comes as a significant problem when an electronic device, e.g. the radio of a car, is assembled on the production lines, because not only many screws have defects, as well the screwing provokes shavings which when in contact with the PCB components may cause mal-functioning due to the creation of non-wanted electrical connections between the components. These problems are difficult to solve when screws are used to secure the parts together. Therefore, the present disclosure meets the demand of auto radios without screws. [0004] There is thus a desire to eliminate the need for the screws usage on the PCB fixation and grounding contact.

[0005] The existent methods do not fulfil the needs of this project due to several aspects. Most of the inventions imply the usage of one or more additional parts, making the assembly process of the auto radio's chassis even more complex and expensive (screws are very cheap additional parts), solving only the shaving problem, making the existent solutions insufficient, expensive, or both.

[0006] Other solutions not only imply the use of additional parts as well do not apply enough load on the PCB, being only applicable on systems as computers (see US6158594A, US20090219703A1 and US7034223) or other devices which do not require such an elevated connection load between its parts.

[0007] An insufficient load between chassis and PCB may allow for vibration and unsecure fastening of the PCB or even the partial or full loss of electrical connection of the ground connection when in movement. A faulty ground connection is a fault that is usually very difficult to diagnose as it may cause erratic and non-permanent failure modes.

[0008] These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.

General description

[0009] The present disclosure relates to a spring for fixation and grounding contact of a printed circuit board (PCB) in a chassis (housing) for electronic components without any additional components. This spring is made by a progressive die on the same sheet metal where the chassis parts are made. This geometry is capable of putting the circuit board under a compressive load to, not only fixate the PCB as well insure the grounding contact using the material spring-back elasticity. The compressive load prevents it from vibrating and bending over the limits, managing to keep all the components intact during a normal use of the chassis, for example as the chassis of an electronic device like the radio of a vehicle.

[0010] The disclosure is capable of dismissing the usage of screws or any other additional part, while still being able to create electrical grounding and apply a contact load large enough to fix the PCB during the component's lifecycle.

[0011] To address the requirements described above, the present disclosure describes a spring capable to connect, with enough force, the PCB to the correspondent chassis while making electrical grounding between them and eliminating the need of any additional parts such as screws and by consequence, eliminating the shavings resulting from the screwing process. The spring designed can replace both the screws and the springs (made in a different process and material from the chassis) in all its functions, such as fixation of the PCB, grounding between the board and the chassis and even between components in the same circuit, so it eliminates the voltage gap between them, with a very rapid and easy mounting. The voltage gap is eliminated due to the electric contact that is created from the PCB to the entire chassis. In case of big voltage peaks the circuit will not be damaged because most of that voltage will be delivered to the chassis. The present embodiments needed a high compressive load such that they hold the PCB in its correct position and absorb the energy resulting from the dynamic solicitations, thus avoiding vibrations due to its spring behaviour.

[0012] To accomplish those goals, it was designed and developed a spring, using only material from the chassis where the PCB is fixated. This spring is embossed with a recess in particular in the format of a "castle" where the contact between the PCB and chassis occurs. The geometry of the recess or embossment has in particular the overall shape of a conical revolution, which is used in automotive sheet metal parts with other purposes, such as for components spacing, as well in auto radios manufacturing to compensate tolerances. The present disclosure is also focused in the geometry around the embossed part, or alternatively referred as built-in or recess. [0013] This geometry around the built-in consists of material removal in the shape of rips, e.g. cut-outs or die-cuts, and it can be configurable depending on the variables to input on the PCB, such as axial force and PCB thickness (or set of tolerances) and the characteristic curve (force vs displacement) of the spring.

[0014] In this geometry it is wanted the usage of the material's springback in order to load the PCB. The surface of the rips will be strained and its elastic energy (springback) will apply the referred load on the PCB, so it will be completely fixated in the normal plan to the recess surface. Before the fastening of the bottom chassis (where the springs are preferably placed) to the top chassis, the PCB is already fastened in all its direction except for the direction normal to the built-in. During the colocation of the bottom chassis, the recess will enter in contact with the bottom surface of the PCB and will be deformed in its normal direction until the bottom chassis reaches its final position. Once it happens, both bottom and top chassis must be fastened to each other. With both chassis fastened, the springback effect on the rips will create a spring-like behaviour in the recess, fixating the PCB on the last direction and absorbing vibration on the same direction. All the other directions are fixated using material from the bottom and top chassis, dismissing the need of spring effect. The energy resulting from dynamic solicitations is absorbed in the remaining axis through the friction load resulting from the compressive load provoked by the spring.

[0015] The spring was configured in particular to be deformed both elastically and plastically, such that the plastic deformation is responsible for the compensation of the dimensional variation, tolerance and assembling clearances; and the elastic deformation is responsible for the permanent compressive force.

[0016] To be noted that the present disclosure can also make the electrical connection between the PCB and the auto radio chassis, dismissing this way the usual small spring used for this situations. [0017] It is disclosed a metal sheet spring for PCB fixation comprising a central embossed part connected by a plurality of die-cut arms to a peripheral part surrounding the central embossed part, wherein the central embossed part, the die-cut arms and the peripheral part are of the same metal sheet, wherein each of the die-cut arms comprises three sections, a first radial section connected to the central embossed part and connected to a second arc-shaped section which is connected to a third radial section which is connected to the peripheral part.

[0018] In an embodiment, the die-cut arms are deformed such as to displace the central embossed part further in the direction of the embossment of said central embossed part.

[0019] In an embodiment, the die-cut arms are deformed such as to obtain a spring having an elastic force against the displacement of the central embossed part against the direction of the embossment of said central embossed part.

[0020] In an embodiment, the metal sheet spring is an electrical contact for the PCB with the spring metal sheet.

[0021] In an embodiment, the metal sheet spring is a grounding electrical contact for the PCB with the spring metal sheet.

[0022] In an embodiment, the direction of the embossment of the central embossed part is perpendicular to the spring metal sheet.

[0023] In an embodiment, the arc-shaped sections of the die-cut arms and the central embossed part are circular.

[0024] In an embodiment, the geometric centre for the radial sections and the arc-shaped sections of the die-cut arms is the geometric centre of the central embossed part.

[0025] In an embodiment, the peripheral part is a surface comprising a circular aperture in which the central embossed part and the die-cut arms are arranged.

[0026] Metal sheet spring for PCB fixation according to any of the previous claims wherein the central raised part is mound-shaped, frustoconical or a pyramidal frustum. [0027] In an embodiment, the number of die-cut arms is four. Alternatively, the number of arms may be 2, 3, 5, 6, 7 or 8. The number of arms can be determined as a function of the requirements in terms of the required characteristic curve (force-displacement curve) of the metal sheet spring.

[0028] In an embodiment, the metal sheet spring is obtainable by die stamping of a single metal sheet.

[0029] In an embodiment, the metal sheet spring is obtainable by progressive die stamping of a single metal sheet.

[0030] In an embodiment, the die-cut arms are obtainable by stamping out a plurality of pierced rips from the metal sheet, wherein said rips are in the same number as the die-cut arms, and wherein each of the pierced rips comprises three sections, a first arc-shaped section connected to a second radial section which is connected to a third arc-shaped section.

[0031] Dimensions of the metal sheet thickness and width of the sections of the die-cut arms may be calculated as indicated above. Preferably the calculation of the width of the sections of the die-cut arms is interrelated with the metal sheet thickness.

[0032] In an embodiment, the thickness of the spring metal sheet is 0.2 - 5 mm, in particular 0.5 - 2 mm.

[0033] In an embodiment, the width of the first radial section of the die-cut arms is 0.2 - 10 mm, in particular 0.5 - 5 mm.

[0034] In an embodiment, the width of the second arc-shaped section of the die-cut arms is 0.2 - 10 mm, in particular 0.5 - 5 mm.

[0035] In an embodiment, the width of the third radial section of the die-cut arms is 0.2 - 10 mm, in particular 0.5 - 5 mm.

[0036] It is also disclosed a metal sheet chassis comprising one or more of the metal sheet springs according to any of the previous claims. [0037] It is also disclosed an automotive radio comprising the metal sheet chassis according to the previous claim.

[0038] It is also disclosed a method for obtaining a metal sheet spring for PCB fixation, said method comprising the steps of:

stamping a central embossed part for the metal sheet spring from a metal sheet part; and stamping out a plurality of pierced rips from the metal sheet such as to form said central embossed part connected by a plurality of die-cut arms to a peripheral part surrounding the central embossed part;

wherein each of the die-cut arms comprises three sections, a first radial section connected to the central embossed part and connected to a second arc-shaped section which is connected to a third radial section which is connected to the peripheral part.

[0039] In an embodiment, the method further comprises the step of deforming the die- cut arms to displace the central embossed part further in the direction of the embossment of said central embossed part.

[0040] In an embodiment, said steps are simultaneously carried out. [0041] In an embodiment, said steps are progressively carried out.

[0042] It is also described a method according to any of the described embodiments for obtaining a metal sheet spring for PCB fixation according to any of the described embodiments.

[0043] It is noted that an embossed part provides a recess or a protrusion, depending on which side of the embossed metal sheet is used as reference, with geometry depending on the material thickness and being also dependent upon press tonnage capacity. Normally, the side wall angle is 45° or less, but maybe higher. The height is normally 2-5 times, in particular 3 times thickness of the material, but maybe higher, in the present disclosure as necessary for ensuring appropriate contact and support of the PCB. Brief Description of the Drawings

[0044] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of present disclosure.

[0045] Figure 1: Schematic representation of a top view of an embodiment of the spring geometry and built-in (10).

[0046] Figure 2: Schematic representation of a side view of an embodiment of the built-in (10).

[0047] Figure 3: Schematic representation of a perspective view of a cross-section of an embodiment of the spring (variations in the sheet metal thickness may not be to scale).

[0048] Figure 4: Schematic representation of a bottom view of an embodiment of the chassis (30) equipped with the springs (31 to 34).

[0049] Figure 5: Schematic representation of a first step of an embodiment of the specified installation method to the auto radio's chassis, punch (40) displaces surface (11, 21) (Fig. 1).

[0050] Figure 6: Schematic representation of a second step in an embodiment of the chassis installation, with the built-in (10) (Fig. 1) deformed and the PCB fixated, begins the displacement of the bottom chassis (30) (Fig. 4) containing the springs 31 to 34 in the normal direction of the PCB's (50) surface.

[0051] Figure 7: Schematic representation of an embodiment with the PCB (50) and the bottom chassis (30) (Fig. 4) in their final position, the surface (21) (Fig. 2) of the built-in (10) (Fig.l) is in contact with the PCB (50), putting it under a load large enough to fasten it.

Detailed Description

[0052] Variations of the spring geometry that have direct effect on the sheet metal will be described, because depending on the purpose, the spring can acquire a different geometry so it behaves differently and more suitable to the task in hand. The geometry presented in Fig. 1 and Fig. 3 was developed to fixate a PCB to the metallic chassis of an electronic device, requiring a heavy compression load for fasten the PCB and hold on with the external solicitations, like for example a car moving, the falls in the manufacturing process (up to 100 G) and a car crash (up to 65 G).

[0053] Despite the complexity of the spring there are two most important factors in the spring elastic constant, the distance (4) between the rip's inside strip (2) and the rip's outside strip (1), and the distance (3) between consecutive outside strips from the rips. As the distance between (3) and (4) increases, the force necessary to elastically deform the spring also increases. The disadvantage of having more material to deform (areas 3 and 4) is that not only the spring will impose and absorb bigger loads, but also during the bottom and top chassis placing it will be needed a huge load to deform the strips, which may cause damage in the PCB and potentially making it impossible to a Human to mount both chassis. Also the amount of material to deform must be calculated so it imposes and absorbs the desired load as well it must have springback displacement big enough so it absorbs the vibration in the desired amplitude. In this case, the string contains four rips (9) containing one inside and outside strip each, however it can contain a large variety of rips always depending on the goal to achieve with the spring, for instance, a smaller number of rips will result in bigger amount of material to deform (areas 3 and 4 will increase) which in turn will result in a higher load imposed on the PCB. The minimum number of rips to have a correct functioning of the spring is two, because it must be a symmetric geometry around the built-in to result in a constant load applied to the PCB. The material of the sheet metal (8) where the spring is made can be a wide range of metals, the material used in the simulation was a 6000 series Aluminum alloy due to its good springback characteristics. In case of the usage of a different material the geometry (number of rips and distance between them) may need to be different in order to have the same spring behaviour. The detachment (5) between the castle superior diameter (7) and the rip's inferior strip (2) has also an important role in the spring elastic behaviour, being directly proportional the detachment (5) and the force necessary to deform the spring.

[0054] Regarding the forming of the embossment (10), its dimensions can obtain various values, according to the application. In this case, once the embossment is responsible for the loading on the PCB by the metal chassis of an auto radio, the dimensions are fairly large, due to the large dimensions of the chassis and PCB in question and the demanding requirements of the automotive application. Anyhow the dimensions can be smaller or bigger depending on the size of the devices to be installed. The disclosure can be applicable in different types of electronic devices which use metallic chassis, such as laptop, mobile phones, desktops, TV's, etc. As shown in Fig. 2 the surface (21) provides the contact amongst the disclosed embossment and the PCB, applying the pressure necessary to fix it. The sheet metal (25) thickness, defined by the distance between (20) and (22), and the built-in depth, defined by the distance between (20) and (21), can also attain different values, accomplishing consequently different spring behaviour. Higher the sheet metal thickness the more force will be necessary to strain the spring (for the same material). The embossment depth is not so important for the spring behaviour but for the distance among the bottom chassis and the PCB, although the smaller the depth the more accurate it will be the effect of the spring, because the embossment strain will have a smaller influence on the spring. In any case the embossment depth is not an important dimension to take into account upon the dimensioning of the spring (the embossment has a much reduced springback effect in comparison with the spring arms). The elements 23 and 24 correspond to the die radius profiles during the stamping of the chassis.

[0055] In the Fig. 4 it is illustrated a practical example that the disclosure has been applied, an auto radio chassis (30), in this case the bottom chassis. The springs described previously 31-34 are placed in the bottom chassis, tactically positioned so it presses in the specified spots in the PCB, to be placed and pressed during the mounting of the bottom and top chassis. [0056] In the auto radios area, due to the restrict package of the chassis embodiment the spring may have a more complex method of installation. In Fig. 5 it is illustrated the first step of the method, where a punch (40) presses the surface (11) (Fig. 1) of the embossment displacing it the required depth, which is about 1mm, depending on the application. As result, the metallic strips will be deformed as shown in figure 6. This operation is meant to maintain the metallic strips within the exterior limits of the chassis when pressed against the PCB.

[0057] Once the embossment is deformed, the next step corresponds to the PCB/chassis placing. Admitting the PCB is fixated using material from the top chassis, it can begin the chassis positioning. As shown in Fig. 6 the surface (21) will enter in contact with the PCB (50), after these two components touch each other, it should be input a displacement on the bottom chassis equal to the displacement input in the embossment deformation (which is said in the previous paragraph to be around 1mm), so the spring deformation does not breaches the embossment package.

[0058] Preferably, it must be ensured the components move only in the direction shown in Fig. 6, this is, in the normal direction to the component's surfaces. The PCB can easily be fixated on the other directions with rigid connections, once the dynamic solicitations absorption will be made by the friction load created on the PCB surface by the normal load to this surface.

[0059] At least, with both the PCB and sheet metal fixated, the spring effect will put the PCB under a force (Fig. 7), so the PCB is correctly fixated and also preventing it from unwanted vibrations that can damage its components. As referred previously, the force value imposed on the PCB by the spring depends on the geometry designed, in this case it was developed a geometry to support an auto radio's PCB, so it was needed a spring with high force (300 N each spring). However it can be designed variations of this geometry to apply much more reduced or elevated forces, depending on the device and the conditions this device must bear in its lifetime. [0060] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0061] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof.

[0062] The above described embodiments are combinable.

[0063] The following claims further set out particular embodiments of the disclosure.