GB2041818A - Encapsulating a Magnetic Domain Component - Google Patents

A method of producing a magnetic domain component comprising a magnetic part within a shield, is described in which the magnetically sensitive parts are encapsulated into the shield by injection or transfer moulding of epoxy or silicone resin, the shape of the component being defined during moulding at least partly by the shield, which is supported within a mould. The shield is located in the mould 1/2 between mould parts 6/9, flashing around the end of the shield being prevented by mould parts 5/8 which are adjustable by screws 11/12. The leads of the magnetically sensitive part are located in recesses 18/19. <IMAGE>

SPECIFICATION Magnetic Domain Component This invention relates to magnetic domain components and is particularly concerned with a method of an apparatus for the production of such components.

A magnetic domain component has several constituent parts. These are usually a chip of magnetic domain material; a pair of coils arranged orthogonally around the chip and a pair of permanent magnets sandwiching the coils and the chip.

In order to protect the magnetically sensitive parts and hence any stored data from stray signals, the component is completed by a magnetic shield within which the other parts reside.

To give the component environmental protection the shield is filled with a plastics material and so far this has been done manually.

Whilst suitable for experimental components manual moulding is not adequate for production runs. This invention seeks to provide a method of making a magnetic domain component in which the above disadvantage of known encapsulation techniques is overcome.

According to one aspect of this invention there is provided a method of manufacturing a magnetic domain component including the steps of encapsulating magnetically sensitive parts of the component within a magnetic shield by injection moulding with a suitable material and in which a peripheral surface of the component is defined during moulding by a surface of the shield.

Any suitable moulding material may be used examples being epoxy, epoxy/silicone or silicone materials.

A suitable form of injection moulding is the transfer moulding process.

The moulding may be carried out in a mould on an injection moulding machine, the mould having a cavity into which the component is located, the cavity having dimensions to allow acceptance of the component shield whilst preventing substantial flashing of moulding material between the shield and the mould.

A two part mould may be used, the two parts together defining the cavity.

One part of the mould may have means for supporting the shield and electrical leads to which parts within the shield are connected in spaced apart relationship to one another.

The mould may include means for adjusting a dimension of the cavity to provide abutment of a surface of the cavity and the shield to a tolerance of within .001" and preferably within .0005".

The shield may be a hollow tubular shield and the adjustable dimension may be in the direction of the length of the shield so as to provide abutment between respective mould surfaces and the open ends of the shield to a tolerance of within 0.001" and preferably less than 0.0005".

According to a second aspect of this invention there is provided a method of manufacturing a magnetic domain component including the steps of assembling magnetically sensitive parts of the component within a hollow tubular shield with electrical leads extending from the shield; supporting the shield and leads in spaced apart relationship in one part of a two part mould; assembling a second part of the mould onto the first part with the two parts substantially abutting respective surfaces of the shield, adjusting an end surface of a cavity defined by the two parts and in which the component resides, until ends of the shield abut respective end surfaces of the cavity; injecting a suitable moulding material on an injection moulding machine to fill the shield and removing the component from the mould.

The invention will now be described further with reference to the accompanying drawings in which: Figure 1 is a sectional elevation of a mould in accordance with an aspect of this invention; and Figures 2 and 3 are respectively plan views of upper and lower halves of the mould of Figure 1 with the two halves folded back to reveal inside mating surfaces.

Referring to Figures 1 to 3 of the drawings there is shown a two part mould for the encapsulation of the magnetically sensitive parts of a magnetic domain component formed by upper and lower bolster plates 1 and 2 respectively which are separable along a mating surface 3. The upper bolster plate 1 has a cavity 4 which carries inserts 5 and 6 whilst the lower bolster plate 2 has a similar cavity 7 which carries inserts 8 and 9. The inserts 5, 6, 8 and 9 define acurately peripheral surfaces of a cavity 10 in which the magnetic domain device sits for encapsulation.

The upper bolster plate 1 is provided with a pair of cap screws 11 which pass through an end of the upper bolster plate to allow a small adjustment in the position of the insert 5 whilst in similar manner the lower bolster plate 2 is provided with a pair of cap screws 12 for adjusting the position of the insert 8. Extending through the inserts 4 and 7 respectively are a pair of ejector pins 13 and 15 which on separation of the bolster plates 1 and 2 after the moulding process may be tapped to eject the completed component.

The upper bolster plate 1 is provided with a moulding material feed hole 15 which extends through the bolster plate 1 and communicates with a U-shaped channel 16 in the lower bolster plate 2 along which the moulding material passes and enters the cavity 10 via a small feed hole 17 which is approximately 0.050" square.

In order to encapsulate a component the magnetically sensitive parts are assembled into a shield which is typically a hollow cylindrical shield of rectangular cross section so that electrical connecting leads extend from each end of the shield. The component is introduced into the mould which is at this stage split along the interface 3 and the component rests with the shield on the insert 7 with the leads supported spaced apart from the shield and seating in grooves 18 and 19 provided repectively in the lower bolster plates 2 and the insert 8.The upper bolster plate is then placed in position so that the insert 4 contacts an upper surface of the shield of the device which at this stage fills the cavity 10 and the two pairs of screws 1 1 and 12 are adjusted to move the inserts 5 and 8 so that cavity end surfaces abut the shield to a tolerance of within 0.001 " and typically to within 0.0005".

To facilitate alignment of the two bolster plates 1 and 2 during assembly of the mould diagonally opposed guide pins 20 are provided to pass through the plates 1 and 2.

After assembly of the mould and adjustment of the cap screws 1 1 and 12 the mould is placed in an injection moulding machine and moulding material is injected into the aperture 15, along the channel 16 and passes into the shield through the aperture 1 7. A transfer moulding machine is preferred and the mould described so far is suitable for use on a Lauffer model VSKO 25 ton transfer moulding press. The moulding pressure and rate of flow of moulding material may be adjusted on the machine so that the shield is completely filled with material whilst at the same time damage to the delicate parts located within the shield is avoided.

Any suitable moulding material may be used but typical materials are of epoxy, epoxy/silicone or silicone form, examples of proprietary materials being Polyset 41 0C (Polyset is a registered trade mark) and Dow Corning 631 semiconductor grade moulding compound.

After moulding the mould is removed from the moulding machine and the upper and lower bolster plates 1 and 2 are separated at the interface 3 and the completed component is removed from the mould if necessary by tapping one or other of the ejector pins 1 3 and 14.

As can be seen by injecting the moulding material at a controlled rate and pressure a solid moulded component is formed in which the material has a good adhesion to the shield. It is therefore possible to achieve a high rate of component production since the high throughput rates of transfer moulding may be utilised and this high throughput is coupled with the environmental protection which is normally associated with semiconductor components. The shape of the component is not defined by the mould cavity as in conventional injection moulding techniques but is defined by the shield and therefore a magnetic domain device package with shield attached is produced in one shot.

Although this invention has been described with reference to the drawings showing a mould for use on a particular transfer moulding machine any convenient form of injection moulding may be used. Similarly any material which may be injection moulded and which provides the required amount of environmental protection may be used for filling the shield.

Other modifications may be made without departing from the scope of this invention. For example although a mould only having a single cavity for accepting a single magnetic domain device component has been described moulds may be used having a number of cavities so that several components can be produced by a single moulding shot.

Claims