Patent Application
20220326469
This application claims priority to Great Britain Patent Application Number 2105071.1, filed Apr. 9, 2021, the disclosure of which is hereby incorporated by reference in its entirety herein.
Cameras and other optical devices are important sensors in automotive applications, particularly with the increasing prevalence of autonomous driving and safety assistance systems. As these systems become more advanced, they have driven the use of higher resolution cameras. However, as a digital camera's resolution increases, it becomes more sensitive to optical misalignment caused by, for example, strain and deformations within the assembly.
In this respect, during assembly of a camera, an imager soldered to a printed circuit board (PCB) may be mechanically secured via the PCB to a lens holder using screws. A lens may then be actively aligned to the imager assembly to align its focal plane with the sensitivity plane of the imager's sensor to provide for the output of a focussed image. Once in its aligned position, the lens is then secured by curing an adhesive at the mounting interface between the lens and the lens holder. As such, this active alignment step of the lens can be used to correct for minor positional variances arising from component manufacturing tolerances. However, as the resolution of imagers increases, even micron level deformations can compromise image clarity. This is a particular problem as the camera assembly is heated and cooled during normal use because residual strains within components may cause flexing in the PCB. Whilst small, these movements arising from thermal cycling may cause parts of the imager to move slightly out of focus by 1 or 2 microns. As such, image focussed is reduced, thereby minimising some of the benefits of using a higher resolution imager. As such, there is a need for further ways to improve the maintaining of focus of an optical system within a camera assembly.
The present disclosure relates to a method of assembling an optical device. The present disclosure also concerns an optical device assembled using the method. The disclosure is particularly relevant to a method of assembling an automotive camera, and the manufacture of camera assemblies for automotive applications.
According to a first aspect, there is provided a method of assembling an optical device, including: providing a circuit board supporting an imager and a support for supporting the circuit board; applying a first adhesive layer to a mating region of at least one of the circuit board and the support; and fastening the circuit board to the support using at least one fastener, wherein the first adhesive layer is compressed between the mating regions once the circuit board is fastened; curing the first adhesive layer for forming a stabilised imager assembly; fixing a lens to the stabilised imager assembly using a second adhesive layer, wherein the step of fixing the lens includes positioning the lens on the support to align its focal plane with the imager and curing the second adhesive layer.
In this way, the imager assembly may be fully stabilised by the cured first adhesive layer before the step of actively aligning the lens. That is, in addition to the standard mechanical fasteners between the imager PCB and the support, an adhesive layer is used to reinforce the fixing by binding together the mating faces of these components. As this adhesive layer reaches its full bonding strength, it thereby stabilises the position of imager relative to the support. Consequently, when the lens is subsequently fitted to the stabilised assembly, the alignment between the lens and the imager may be maintained. For example, even if strains manifest around screw fasteners due to thermal cycling, the adhesive bonding between the PCB and the support would prevent these strains from deforming the PCB. This thereby allows positional accuracy to be maintained.
In embodiments, at least one of the steps of curing the first and second adhesive layers includes heating the adhesive. In this way, a heat cured adhesive may be used to ensure complete curing and maximum bond strength between fixed components.
In embodiments, the step of curing the first adhesive layer includes curing until full strength. In this way, the maximum bond strength is achieved between the circuit board and the support to stabilise the assembly before the subsequent alignment step.
In embodiments the step of curing the first adhesive layer includes heating to a temperature equal to or greater than a maximum operating temperature for the optical device. In this way, the curing temperature is selected to be above the operating conditions of the device. This may thereby ensure the positional relationship between components is not reduced during normal use.
In embodiments the step of curing the first adhesive layer includes heating for a duration until full cure of the adhesive.
In embodiments, the cured first adhesive layer stabilises the interface between the mating regions in the stabilised imager assembly. In this way, the opposing faces of the circuit board and the support that engage with one another when the circuit board is secured to the support are bonded together by the adhesive.
In embodiments, the step of fixing the lens to the stabilised imager assembly includes optical system alignment for compensating for manufacturing tolerances. In this way, the lens may be optically aligned to the imager for compensating for any positional variances arising from the components, whilst the cured first adhesive layer in the stabilised imager assembly ensures positional accuracy of the imager is subsequently maintained.
In embodiments, the step of fastening the circuit board to the support using at least one fastener includes fastening using a screw fastener.
In embodiments, the step of fixing the lens to the stabilised imager assembly includes aligning the lens based on a cured position of the imager in the stabilised imager assembly.
In embodiments, the first adhesive layer surrounds the imager. In this way, the first adhesive layer provides a fixing to the support which encircles the imager. In embodiments, the first adhesive layer is radially closer to the imager than the fastener. In this way, the distance over which the circuit board may flex is reduced.
According to a second aspect, there is provided an optical device including: a stabilised imager assembly including a circuit board supporting an imager, a support for supporting the circuit board, and at least one fastener fastening the circuit board to the support, wherein the fastening is stabilised by a first adhesive layer of cured adhesive compressed between mating regions of the circuit board and the support; and a lens fixed to the support by a second adhesive layer of cured adhesive in a position so that its focal plane is aligned with the imager in the position stabilised by the first adhesive layer.
In this way, an improved optical device, such as a camera, may be provided in which the lens has been aligned to the position of the imager in a pre-stabilised assembly. That is, the imager's position relative to the support is fixed by the cured adhesive prior to alignment of the lens. This thereby allows focus to be maintained in the resultant assembly.
In embodiments, the adhesive is heat cured.
In embodiments, the first adhesive layer is cured to full strength, and the focal plane is aligned with the imager in the position stabilised by the full strength cured first adhesive layer.
In embodiments, the first adhesive layer is cured to full cure, and the focal plane is aligned with the imager in the position stabilised by the full cured first adhesive layer.
In embodiments, the cured first adhesive layer stabilises the interface between the mating regions in the stabilised imager assembly.
In embodiments, the lens is fixed to the support for compensating for manufacturing tolerances in optical system alignment.
In embodiments, the at least one fastener includes a screw fastener.
An illustrative embodiment will now be described with reference to the accompanying drawings in which:
The PCB 1 is seated into a recess provided in the base of the lens holder 4. Once seated, an imager mating region 2 on the PCB 1 mates with an opposing holder mating region 3 of the lens holder 4. As shown in
The lens 6 is provided with a radial collar 7 which is used to secure to the lens 6 to a lens seat 5 provided at the front of the lens holder 4. The collar 7 fixed in place by a second adhesive layer 8. The lens seat 5 and the collar 7 provide mating regions between the lens 6 and lens holder 4 for aligning the lens 6 to the imager 10.
During assembly, a bead of adhesive is applied to the imager mating region 3 of the lens holder 4 to form the first adhesive layer 9. The PCB 1 containing the imager 10 is then fitted to the lens holder 4 and fixed in place by the screw 11. The screw 11 passes through a screw aperture in the PCB 1 and the screw's head presses the PCB 1 against the housing 4. This acts to compress the first adhesive layer 9 between the holder mating region 3 and the opposing imager mating region 2 on the surface of the PCB 1. Once the PCB 1 is mechanically fixed by the screws, the first adhesive layer 9 is heat cured until it achieves full cure and attains its full bonding properties. This thereby acts to stabilise the PCB 1 relative to the lens holder 4, and hence also stabilises the imager 10 soldered to the PCB 1.
Once the first adhesive layer 9 has fully bonded, a stabilised imager assembly 12 is formed which includes the PCB 1, the imager 10 and the lens holder 4. The lens 6 may be fixed to the lens holder 4 in an active alignment step to align the optical system. For this, a bead of adhesive is applied between the seat 5 and the collar 7 to form the second adhesive layer 8, and the position of the lens is adjusted until the focal plane of the lens 6 is optimally aligned for focussing an image onto the imager 10. The second adhesive layer 8 is then UV cured to fix the lens 6 in the aligned position relative to the lens holder 4. Thermal curing may then be used to fully cure the second adhesive layer 8 and achieve maximum bonding strength.
Importantly, because the active alignment step occurs after the imager assembly has been stabilised by the cured first adhesive layer 9, the positional stability of the imager 10 may be maintained. As such, the resultant camera assembly is less prone to defocussing arising from positional changes between the imager 10 relative to the lens 10 because the position of the PCB 1 is stabilised by its more secure fixing to the lens housing 4. This, in turn, stabilises the final optical system when subjected to thermal cycling during normal camera use.
It will be understood that the embodiment illustrated above shows an application only for the purposes of illustration. In practice, embodiments may be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement.
In this connection, for example, whilst the above illustrative embodiment utilises heat curing for the first adhesive layer 9, it will be understood that other curing methods, such as UV curing, may be used. Furthermore, it will be understood that the first and second adhesive layers may be the same type of adhesive, or in other embodiments different adhesives may be used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2105071.1 | Apr 2021 | GB | national |
