GB2464475A

GB2464475A - Protection for electronic components by in-situ encapsulation

Info

Publication number: GB2464475A
Application number: GB0818860A
Authority: GB
Inventors: Ian Martin Cottom
Original assignee: Haldex Brake Products Ltd
Current assignee: Haldex Brake Products Ltd
Priority date: 2008-10-15
Filing date: 2008-10-15
Publication date: 2010-04-21
Anticipated expiration: 2028-10-15
Also published as: GB0818860D0; GB2464475B

Abstract

A method of protecting electronic components 16a' and 16b' including the steps of mounting the electronic components 16a' and 16b' in a housing 22', injecting a quantity of polymeric potting material 28, preferable polyurethane, into the housing 22' through a port 24' in the wall of the housing 22, the quantity being less than that required to fill the housing 22', and rotating or vibrating the housing 22' so that the potting material 28 forms a coating on the electronic components 16a' and 16b'. Once the material 28 has been injected into the housing 22' the port 24' is closed by mounting a gas permeable cap 32 over it and the housing 22' is placed in an oven so to cure the material 28. This method is suitable for encapsulating an electronic control unit within a housing such that the unit is protected from corrosion to prevent premature failure of the components.

Description

Title: Method of Protecting Electronic Components

Description of Invention

The present invention relates to a method of protecting electronic components, particularly but not exclusively those used in controlling operation of a vehicle, from environmental damage.

It is known to provide electronic control of various aspects of operation of a vehicle. For example, electronic engine management, braking, suspension, cooling and lubricating systems are known. A vehicle is therefore typically provided with an electronic control unit (ECU) to control one or more of these electronic systems, and the ECU may be mounted on the underside of the vehicle chassis, where it is exposed to spray from the road surface whilst the vehicle is in operation. If unprotected, the spray could cause corrosion of electronic components in the ECU, which could lead to the premature failure of the ECU. This problem is particularly significant where the vehicle is exposed to salts or salty water, for example where the vehicle is used in cold climates and where salt is spread on the road surface to reduce the risk of ice formation.

It is therefore imperative to protect the delicate electronic components of the ECU from such damage, and conventionally the ECU is mounted in a housing, the gaps between the housing and the ECU being completely filled with a polymeric sealing material, so that the electronic components of the ECU are encased in the polymeric sealing material. This process is known as "potting", and the polymeric sealing material as the "potting material". The potting material is typically a thermosetting polymer which is injected into the housing in its fluid, uncured form, and, once the housing is completely full, the entire unit is placed in a temperature controlled environment for sufficient time to * 2 cure the potting material. During the curing process, forces are exerted on the ECU due to distortions in and shrinkage of the potting material. This can cause delamination of the potting material from the ECU, and wires extending between electronic components of the ECU, for example between components on an electronic circuit board, to be pulled away from their respective connections. Where this potting process is used, it is therefore necessary to take steps to ensure that the strength of the soldered joints in the ECU is sufficient to withstand these forces.

According to a first aspect of the invention we provide a method of protecting an electronic component including the steps of mounting the electronic component in a housing, placing a quantity of liquid polymer into the housing, the quantity being less than that required to fill the housing, and moving the housing so that the polymer forms a coating on the electronic component.

By virtue of the invention, the electronic components can be sealed in the housing and protected from ingress of environmental contaminants such as road spray, whilst the weight of the resulting assembly, and the time taken to complete the potting process, is reduced compared to an assembly formed using the prior art method. The invention has the further advantage that the process requires less potting material than the prior art process, and is therefore cheaper in terms of materials costs. Moreover, as the potting mixture forms only a relatively thin coating on the ECU, and not a solid mass within the housing, the shrinkage and distortion of the potting material is reduced significantly compared to the prior art method. Delamination of potting material from the ECU is virtually eliminated, and strengthening of the solder joints in the ECU is not required to avoid damage to the ECU.

Preferably the housing is rotated so that the polymer forms a coating on the electronic component. Alternatively, the housing may be vibrated so that the polymer forms a coating on the electronic component.

The method may further include the step of, after moving the housing so that the polymer forms a coating on the electronic component, placing the resulting housing and electronic component assembly in an oven and heating to cure the polymer.

Preferably the polymer is injected into the housing through a port provided in a wall of the housing. In this case, the method may further include the step of, after injecting the polymer into the housing, mounting a cap on the port to substantially close the port. The cap may be porous so that it substantially prevents liquid polymer from leaking from the housing during the movement of the housing whilst allowing gases to pass out of and into the housing. This is particularly advantageous where the polymer is cured using heat. If the cap provided a gas tight seal, the expansion of gases within the housing during the curing process would cause excess pressure to build up in the housing, which could put the housing and electronic component under undesirable stress, damage the housing or electronic component or even blow the cap off.

Where a cap is mounted on the port after injection of the polymer into the housing, this cap may be removed, and a second cap mounted on the port after moving the housing so that the polymer forms a coating on the electronic component. In this case, the second cap may be porous.

The polymer may, for example, comprise polyurethane.

According to a second aspect of the invention we provide an electronic device comprising a housing having an interior in which are mounted a plurality of electronic components, wherein the electronic components and interior surfaces of the housing are coated in a layer of polymeric resin, there being a space between the coating on the electronic components and the coating on the interior surfaces of the housing.

The electronic device may be an electronic control unit configured to be used in a vehicle to control at least one aspect of operation of the vehicle. The electronic control unit may, for example, be a braking control unit. The electronic device may, alternatively be an electronic diagnostic unit for viewing or extracting data concerning the operation of a vehicle.

The electronic device is preferably formed using the method of the first aspect of the invention.

An embodiment of the invention will now be described with reference to the accompanying drawing of which FIGURE 1 shows a partial cross section through a prior art braking control unit, and FIGURE 2 shows a cross section through a braking control unit for a vehicle made according to the first aspect of the invention.

Referring now to Figure 1, there is shown a prior art braking control unit 10, which in this example has an electronic control unit (ECU) 12 and a valve block 18 comprising a plurality of valves. The ECU 12 comprises a plurality of electronic circuit boards (ECB) 14 and a plurality of electronic control components including the connection to each external electrical pin 16, and connections between the ECB 14 and a plurality of solenoids 20 by means of which the valves may be operated to control flow of compressed air to and from a plurality of brake actuators. The ECB 14, electronic components 16a, 16b and solenoids 20 are all mounted in a generally rectangular housing 22, having a base 22a, four side walls 22b and a lid 22c, and the spaces between the ECB 14, electronic components 16a, 16b, solenoids 20 and the housing 22 are filled with a cured polymeric potting material 26.

A generally circular aperture is provided in one of the side walls 22b of the housing, to form a potting port, and this prior art braking control unit 10 is formed by mounted in the ECB 14, the electronic control components 16a, 16b and solenoids 20 in the housing, and injecting the uncured polymer, in liquid form, through the potting port 24 into the housing 22 until the housing 22 is completely full of liquid polymer. The potting port 24 is then sealed, and the entire assembly left at room temperature for sufficient time to allow the polymer to cure. The assembly may, alternatively be placed in an oven and heated to an appropriate temperature and for an appropriate time to allow the polymer to cure. The ECB 14, electronic control components 16a, 16b, and solenoids 20 are therefore embedded in a solid block of resin which minimises ingress of water or other contaminants into the braking control unit 10, and hence assists in reducing the likelihood of corrosion or damage to the ECB 14 or electronic control components 16a, 16b.

The weight of the resulting block of resin can be significant, and its size means that, during the curing process, internal stresses can build up in the resin block 26, which distort and, in places, pull away from the surfaces of the ECBs 14 electronic components 16a, 16b, solenoids 20 or housing 22. Where the resin pulls away from the surfaces of the ECBs 14, this can cause some of the delicate wires connecting electronic components in the ECU 12 to be broken or pulled away from their respective connections. Moreover, the resulting space between the resin block and the ECU 12 provides a means for water to penetrate the braking control unit 10 and come into contact with the ECU 12.

Referring now to Figure 2, there is shown a second braking control unit 10', this one made according to the first aspect of invention. The second braking control unit 10' includes exactly the same arrangement of ECU 12', valve block 18', solenoids 20' and housing 22' as the prior art braking control unit 10, but, in this case, the ECBs 14', electronic control components 16a, 16b, and solenoids 18' are not embedded in a solid block of polymer resin. Instead, the ECB 14', electronic control components 16a', 16b', solenoids 20' and interior surfaces of the housing 22' are covered in a polymer coating, there being spaces 30 between coating 28 on the housing 22' and the coating on the ECB 14', electronic control components 16a', 16b', and solenoids 20' in at least places in the housing 22'. * 6

A side wall 22b' of the second braking control unit 10' is provided with a generally circular aperture which also provides a potting injection port 24', and the braking control unit 10' is formed by mounting the ECB 14', electronic control components 16a', 16b', and solenoids 20' in the housing 22', and injecting a quantity of uncured polymer, in liquid form, through the potting injection port and into the housing 22'. The quantity of polymer used is not, however, sufficient to fill the housing. In this example 400g of polymer is used and this fills around one third of the free volume in the housing 22'.

Once the polymer has been injected into the housing 22', the potting injection port 24' is closed using a first cap 32, and the braking control unit 10' moved so that the polymer forms a generally even coating on all the exposes surfaces of the ECB 14', electronic control components I 6a', 1 6b', and solenoids 20', and interior surfaces of the housing 22. It has been found that the best way to form such a coating is to rotate the braking control unit 10', and in this example, the braking control unit 10' is rotated three times about a single axis at a rotational speed of 1 rpm. The coating process may be carried out a different way, however, -by vibrating the braking control unit 10', for example.

Once the coating is formed, the cap 32 is replaced by a porous plug and the braking control unit 10' is placed on its lid 22c, i.e. with the base 22a vertically above the lid 22c', whilst the polymer is cured. In this example, a thermosetting resin which cures at room temperature is used. In this example, the polymer used is a two-part polyurethane, and the polymer is cured at room temperature for 30 minutes. The exact curing regime will, of course, depend on the polymer used, and may involve the application of UV light and/or heat.

Where the application of heat is required the braking control unit 10' is placed in an oven, and heated to an appropriate temperature for an appropriate length of time.

In this example, the porous plug comprises a Gortex membrane with a stainless steel protective pressing. Use of a porous membrane is important as it allows gas to pass into and out of the housing 22' as the temperature within the housing 22' rises and falls, and use of a breathable water proof material such as Gortex is also advantageous as it will prevent ingress of water into the housing 22' via the potting port 24' when the braking control unit lOis in use.

It should be appreciated that whilst the invention is described above in relation to a braking control unit, it may be applied to a diagnostic unit for a vehicle braking system, any vehicle electronic control unit, or, in fact, any electronic device in which it is required to protect the electronic components from the environment.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. O 8

Claims

CLAIMS1. A method of protecting an electronic component including the steps of mounting the electronic component in a housing, placing a quantity of liquid polymer into the housing, the quantity being less than that required to fill the housing, and moving the housing so that the polymer forms a coating on the electronic component.
2. A method according to claim 1 wherein the housing is rotated so that the polymer forms a coating on the electronic component.
3. A method according to claim 1 wherein the housing is vibrated so that the polymer forms a coating on the electronic component.
4. A method according to any preceding claim wherein the method further includes the step of, after moving the housing so that the polymer forms a coating on the electronic component, placing the resulting housing and electronic component assembly in an oven and heating to cure the polymer.
5. A method according to any preceding claim wherein the polymer is injected into the housing through a port provided in a wall of the housing.
6. A method according to claim 5 wherein the method further includes the step of, after injecting the polymer into the housing, mounting a cap on the port to substantially close the port.
7. A method according to claim 6 wherein the cap is gas permeable.
8. A method according to claim 6 wherein the method further includes the step of removing the cap after moving the housing so that the polymer forms a coating on the electronic component, and placing a second cap on the port.
9. A method according to claim 8 wherein the second cap is gas permeable.O
10. A method according to any preceding claim wherein the polymer comprises polyurethane.
11. An electronic device comprising a housing having an interior in which are mounted a plurality of electronic components, wherein the electronic components and interior surfaces of the housing are coated in a layer of polymeric resin, there being a space between the coating on the electronic components and the coating on the interior surfaces of the housing.
12. An electronic device according to claim 11 wherein the electronic device is an electronic control unit configured to be used in a vehicle to control at least one aspect of operation of the vehicle.
13. An electronic device according to claim 11 wherein the electronic device is an electronic diagnostic unit for viewing or extracting data concerning the operation of a vehicle.
14. An electronic device according to any one of claims 11 to 13 wherein the electronic device is formed using the method of any one of claims 1 to I 0.
15. A method substantially as hereinbefore described with reference to the accompanying drawings.
16. A electronic device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
17. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.