TECHNICAL FIELD
The subject matter described herein, in general, relates to potting of an Electronic Assembly contained in a printed wiring board (PWB) and in particular, relates to a method of potting the PWB assembly that eliminates the use of a plastic case used to hold the assembly, thus making it a caseless potting.
BACKGROUND
Printed circuit boards (PCBs) or printed wiring boards assemblies (PWBs) are well known and widely used for implementation of Electronic circuits in different types of control units. Typically, a PWB assembly includes electrical or electronic components for performing various functions and is electrically corrected by soldering or by other means. In the applications where the PWB assembly needs to be protected from the outside environment, such as vibration, humidity etc the units are placed in a receiving case 8c are potted using suitable resin usually of Epoxy or Polyurethane base.
Therefore, to provide protection to a PWB assembly, the PWB assembly is confined in a plastic case and is covered by resin paired all over it. As and when the resin is cured, a potted assembly is formed that includes the PWB assembly, the plastic case, and the solidified resin. This shows that the plastic case becomes an integral permanent part of the potted PWB assembly. However, in many cases it is observed that in due course of time due to environmental factors like thermal cycling, vibration, etc the adhesion between the cured resin and the plastic case gets loosened forming a gap between the resin and case. Hence there are chances of water ingress between the two that may impair proper functioning of the PWB Assembly.

SUMMARY
The subject matter described herein is directed to a method of potting a printed wiring board (PWB) assembly without affixing the case used to pot the PWB assembly thereto. The drawbacks of the conventional method of potting, arising due to the use of a potting case, are overcome by eliminating the use of the case, thereby providing for case less potting. The method of caseless potting described herein is achieved by employing a reusable container.
A typical PWB assembly includes electronic components fixed on a PWB and combined to form an electronic circuit. The PWB assembly is centrally placed in a reusable container using a locator. The reusable container is placed in a support cavity. A mounting lug is attached to the reusable container. Resin is pored over to the PWB assembly placed in the reusable container. As and when the resin is cured, the PWB assembly, the mounting lug along with the solidified resin takes the form of a solid mass referred to as a pot. The pot is separated from the reusable container, i.e., the PWB assembly is completely confined in the solidified resin, thus making the PWB assembly protected from the external environment and damages, and without being held by any external casing. After the pot is separated fi"om the reusable container, the container is ready to be used in another potting process. The, elimination or removal of the plastic case after forming the potted assembly, provides an improved reliability to the PWB assembly by avoiding water to ingress between the case and the potting material. Moreover, eliminating the plastic case is cost effective and environment friendly as a reusable plastic case is used over and over again.
Further, the potted assembly can be affixed onto machinery by using either a mounting lug or a rubber boot. The mounting lug is attached to the reusable container at the time of pouring of resin. Whereas, the rubber boot is mounted on the potted assembly after the resin is

cured and the potted assembly is obtained. In potted assemblies wherein the mounting is done using the rubber boot, affixing of the mounting lug in the potted assembly is optional.
These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
BRIEF DESCRIPTION OF DRAWINGS
The above and other features, aspects, and advantages of the subject matter will become better understood with regard to the following description, appended claims, and accompanying drawings where:
Fig. la illustrates an exemplary PWB assembly.
Fig. lb illustrates an exemplary locator for facilitating right positioning of the exemplary PWB assembly of Fig. la.
Fig. Ic illustrates the PWB assembly mounted on a pair of locators.
Fig. Id illustrates an exemplary mounting lug utilized for mounting a potted assembly.
Fig. 2a illustrates an exemplary reusable case.
Fig. 2b illustrates an exemplary support cavity.
Fig. 2c illustrates embodying the reusable case in the support cavity.

Fig. 2d illustrates embodying the reusable case in the support cavity with the PWB Assembly..
Fig. 3a illustrates the PWB placed in the reusable case placed in the support cavity with the mounting lugs in position..
Fig. 3b illustrates the PWB in the reusable case after pouring the resin.
Fig. 4a illustrates a perspective top view of the potted assembly after removal of the reusable case.
Fig. 4b illustrates a perspective side view of the potted assembly with a boot to facilitate mounting instead of mounting lug.
Fig. 5 illustrates an exemplary method of forming a caseless potting with a mounting lug. Fig 6 illustrates an exemplary method 600 for forming a potted assembly with a rubber boot.
DETAILED DESCRIPTION
Printed wiring board (PWB) assemblies are well known and widely used for implementation of Electronic circuits in different types of control units. In order to provide protection to the PWB assembly, the PWB assembly is potted. The subject matter described herein is directed towards a method of potting. The PWB assembly is confined in a reusable container fitted with a mounting lug, and the PWB assembly is covered by resin poured all over it. As and when the resin is cured, a potted assembly is formed that includes the PWB assembly, the mounting lug and the solidified resin. The reusable container is separated from the potted assembly and may be reused for potting another PWB assembly.

In one embodiment, one or more locators are attached to the PWB before placing it within the reusable container. In yet another implementation, instead of or in addition to, the mounting pads, a rubber boot is attached to the potted assembly for fixing the potted assembly to machinery.
Fig.l shows an exemplary PWB assembly 100. The PWB assembly 100 includes a plurality of electronic components, collectively called as components 102, embedded on a PWB. The electronics components 102 may include resistors, capacitors, semiconductor devices, inductors, etc.
Fig lb illustrates an exemplary locator 104 utilized for supporting and positioning the PWB assembly 100 during potting of the PWB assembly 100. The locator 104 is used to position the PWB assembly 100 centrally inside a reusable container, which is described later in the description, and to elevate the PWB assembly 100 when the PWB assembly is placed inside the reusable container. Fig. Ic illustrates an exemplary embodiment illustrating the PWB assembly 100 mounted on the locator 104. The locator 104 can be made of any material including plastic, metal, and so on. Fig. Id illustrates an exemplary mounting lug 106 having a clamp 108 and an opening 110. The clamp 108 of mounting lug 106 is located in the reusable container. The mounting lug 106, details of which will be described later in the description, is utilized for fastening a potted PWB assembly onto a machinery. The mounting lug 106 is usually a made of plastic.
Fig. 2a illustrates an exemplary reusable container 200. The reusable container 200 may be of any desired shape and is made of any one or more of plastic. Poly Ethylene etc. The reusable container 200 is placed in a support cavity. Fig. 2b illustrates an exemplary support

cavity 202. The support cavity 202 can be of any desired shape in line with the shape of the reusable container and made of any one or more of metal, wood, plastic, etc. In one preferred embodiment, the support cavity 202 is made of aluminum.
The support cavity 202 is utilized to support the reusable container 200. Fig. 2c illustrates an exemplary embodiment showing the position of the reusable container 200 in the support cavity 202. In one implementation, the bottom of the support cavity 202 is inclined at an angle in order to give an inclined position to the reusable container 200.
Fig.2d illustrates an exemplary embodiment showing the position of the PWB assembly 100 in the reusable container 200. The PWB assembly 100 attached to a pair of locators 104 is placed in the reusable container 200. The reusable container 200 is already placed in the support cavity 202. The pair of locators 104 gives an elevated position to the PWB assembly 100 in the reusable container 200 in order to avoid the PWB assembly 100 to touch the bottom or sides of the reusable container 200.
Fig. 3a illustrates placing a mounting lug 106 onto a reusable container 200. The mounting lug 106 is located at the sides of the reusable container 200 with the help of the clamp 108. In one implementation, a plurality of mounting lugs 106 are fixed onto the reusable container.
After the mounting lugs are placed in the reusable container 200, resin is poured on the PWB assembly 100 placed in the reusable container 200. Fig 3b illustrates an exemplary embodiment wherein resin 300 has been poured onto the PWB assembly 100. The resin 300 is poured in such a manner that it covers the electronic components 102 and that the reusable container 200 is filled with the resin 300. The resin 300 also flows to the bottom of the PWB

assembly 100 as the PWB assembly 100 is held with the help of the locators 104. The height of the locators 104 is designed in order to keep all the components 102 inside the reusable container 200, yet adequately elevated above the bottom surface of the reusable container 200 . In one implementation, the bottom of the support cavity 202 is inclined at an angle in order to make the position of the reusable container 200 inclined. This inclined position of the reusable container 200 facilitates variable thickness of resin 300 along the length of the PWB assembly 100. In one preferred implementation, the resin 300 is epoxy resin. In yet another implementation, the resin 300 is mixed with a hardener and is then poured over the PWB assembly 100 in the reusable container 200.
The PWB assembly 100 gets embedded in the resin 300. The resin 300 is cured and takes the shape of the reusable container 200 with the PWB assembly 100 embedded in the resin 300, thus forming a potted assembly. The reusable container 200 is now removed from the potted assembly. The potted assembly includes the PWB assembly 100 embedded in the hardened resin 300.
In one implementation, a mounting lug 106 is placed to a side of the reusable container 200, before pouring the resin onto the PWB assembly 100. The mounting lug 106 is located to the reusable container using a clamp 108. Subsequently, the resin 300 is poured in the reusable container 200 in such a manner that it covers all the electronic components 102 and the clamp 108 of the mounting lug 106 and that the reusable container 200 is filled with the resin 300. The PWB assembly 100 gets embedded in the resin 300 along v^th the clamp 108 of the mounting lug 106, leaving the opening 110 outside to facilitate mounting. The resin 300 is cured and takes the shape of the reusable container 200 with the PWB assembly 100 and the mounting lug 106 embedded with the resin 300, thus forming a potted assembly with moimting lug 106 becoming

an integral part of the potted assembly. The reusable container 200 is now removed from the potted assembly. The potted assembly includes the PWB assembly 100 and the mounting lug 106 embedded in the hardened resin 300. The mounting lug 106 is utilized for fixing the potted assembly onto a machinery.
In yet another implementation, elaborated later in the description, a rubber boot, is used for fixing the potted assembly to a machinery. The rubber boot is mounted on the potted assembly and the potted assembly can be fixed on any machinery with the help of the rubber boot. In such an implementation, the mounting lug 106 may not be provided with the potting assembly.
Fig. 4a illustrates an exemplary embodiment of the potted assembly 400 formed with the PWB assembly 100 embedded in the resin 300. This potted assembly 400 is obtained after removing the reusable container 200. In one exemplary implementation, the reusable container 200 is made of Poly Ethylene that does not adhere to the resin 300. In one embodiment, the potted assembly 400 is provided with the mounting lug 106, affixed to the potted assembly 400, to facilitate mooting of the potted assembly 400. In one embodiment, the potted assembly 400 is provided with another means for mounting. One example of such a means for mounting is a rubber boot.
Fig 4b illustrates an exemplary embodiment of the potted assembly 400. A rubber boot 402 is fixed around the potted assembly 400. The rubber boot 402 enables to mount the potted assembly 400 for fiirther use with some machinery.
Fig 5 illustrates an exemplary method 500 for forming a potted assembly without affixing a plastic case.

At block 502, a printed wiring board (PWB) assembly is taken and locators are fitted on opposite edges of the PWB. The PWB assembly includes electronic components embedded on the PWB. In one implementation, the locators are fitted on diagonally opposite edges of the PWB.
At block 504, a reusable container is placed in a support cavity. The reusable container has a predetermined shape and is made of one or more of plastic. Poly Ethylene etc. The support cavity has a predetermined shape and is made of one or more of metal, wood, plastic etc. In one implementation, the bottom of the support cavity is inclined at an angle in order to place the reusable container in an inclined manner.
At block 506, the PAVB assembly along with the locators, is placed in the reusable container. A mounting lug is attached to a side of the reusable container. In one implementation, the locators are used for centrally placing the PWB assembly in the reusable container and to make the PWB assembly elevated for further processing. In yet another implementation, the mounting lug is metallic and a plurality of mounting lug can be used.
At block 508, a mixture of resin and a hardener is poured over the PWB assembly in the reusable container. In one implementation, the bottom of the support cavity is inclined at an angle in order to place the reusable container in an inclined manner. This inclined position of the reusable container facilitates variable thickness of the resin around the PWB assembly in accordance with the height of the electronic components embedded on the PWB.
At block 510, the reusable container is removed after the resin gets hardened and the PWB assembly gets completely embedded in the resin. The resin gets hardened and attains the

shape of the reusable container with the PWB assembly embedded in the hardened resin and a potted assembly is obtained.
In one implementation, the potted assembly includes the hardened resin having the PWB assembly embedded in the resin.
The reusable container is separated from the potted assembly and hence, the reusable container can be reused to obtain another potted assembly. This reduces the cost of manufacturing of the potted assembly and is also environment friendly as the same reusable container is used over and over again.
Fig. 6 illustrates an exemplary method 600 for forming a potted assembly without affixing a plastic case and mounting a rubber boot onto the potted assembly for fixing the potted assembly to a machinery.
The method depicted for Fig. 6 is exactly similar to the method already described in Fig. 5. The only difference between method 500 and method 600 described herein is that in method 600 the mounting lug is not used, whereas method 500 uses mounting lugs for mounting the potted assembly. Instead, in method 600 the PWB assembly is potted without the mounting lug and after the potted assembly is obtained, a rubber boot is mounted onto the potted assembly for fixing the potted assembly to a machinery.
The previously described version of the subject matter and its equivalent thereof have many advantages, including those which are described above.
Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and

scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.

1/ we claim:
1. A method of potting a Printer Wiring Board (PWB) assembly, comprising:
placing the PWB in a reusable container
fixing a mounting lug on a side of the reusable container;
pouring a resin over the PWB; and
removing the reusable container after the resin solidifies.
2. The method of claim 1, wherein said PWB is supported by a locator to keep the PWB assembly not to touch the bottom or side of reusable container.
3. The method of claim 1 wherein said reusable container is made of plastic.
4. The method of claim 1, wherein said reusable container is placed in a support cavity.
5. The method of claim 1, wherein said mounting lug is plastic.
6. The method of claim 4, wherein said support cavity is made of one or more of metal, wood and plastic.
7. The method of claim 1, wherein said resin is epoxy resin.
8. The method of claim 1, wherein said resin is a polyurethane resin.

9. A method of potting a Printer Wiring Board (PWB) assembly, comprising:
placing the PWB in a reusable container; pouring a resin over the PWB;
removing the reusable container after the resin solidifies and obtaining a potted assembly; and
providing a rubber boot on the potted assembly.
10. The method of claim 9, wherein said PWB is supported by a locator to keep the PWB
assembly not to touch the bottom or side of reusable container.