Molded package

Abstract

A package is manufactured by placing a substrate, for example a lead frame, in a mold with a protection flange extending into a notch in the substrate around a contact surface. The protection flange impedes molding compound from reaching the contact surface reducing the need for a deflash step.

Claims

1. A package, comprising: a substrate having a contact surface and a notch, the notch extending around and below the contact surface and having an inner edge adjacent to the contact surface; and package walls on the substrate around the contact surface and around the notch, the package walls extending into the notch, extending away from the contact surface plane, and having an inner surface at an angle in a range of about 25 to about 90 to the contact surface, the inner surface of the package walls spaced apart from the inner edge of the notch and the contact surface.

2. The package according to claim 1, wherein the inner surface is at an angle in a range of about 25 to about 85 to the contact surface.

3. The package according to claim 1, wherein the inner surface is at an angle of 90 to the contact surface.

4. The package according to claim 1, further comprising a metal layer on the contact surface.

5. The package according to claim 1 further comprising a device mounted on the contact surface.

6. The package according to claim 5, further comprising an encapsulant around the device.

7. The package according to claim 1, wherein the substrate has a metal coating on the contact surface.

8. The package according to claim 7, wherein the metal coating comprises at least one of, iron, or gold, or nickel, or palladium, or silver, or copper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will now be described in detail with reference to the accompanying drawings, in which

(2) FIG. 1 shows a step in the manufacture of a package according to a first embodiment of the invention;

(3) FIG. 2 shows a package manufactured in this way;

(4) FIG. 3 shows a packaged device using the package of FIG. 2;

(5) FIG. 4 shows a package according to a second embodiment of the invention;

(6) FIG. 5 shows a step in the manufacture of a comparative example; and

(7) FIG. 6 shows a package manufactured according to the comparative example.

(8) The drawings are not to scale. Like or corresponding components are given the same reference numbers in the different figures and the explanation relating thereto is not necessarily repeated.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) In a first embodiment of the invention, referring to FIG. 1, a substrate 10 in the form of a conductive lead frame of shaped metal has opposed first 16 and second 18 major surfaces. A contact surface 12 is provided on the first major surface and a notch 14 extends around the complete circumference of the contact surface extending from the first major surface towards the second major surface.

(10) A metal coating 20 is provided on the contact surface 12. The metal coating may be for example iron, gold, nickel, palladium, silver or copper.

(11) The contact surface is a surface of the substrate which contacts the device. Note that the contact surface 12 is not a single connected contact surface with a single connected metal coating 20. Instead, there are a number of gaps 26 in the contact surface 12 to allow the contact surface to provide a number of distinct contacts, including a device mounting surface 22 to which the device will be bonded in the finished device and a number of bond pads 24, only one being illustrated in FIG. 1. In the embodiment shown the gaps 26 are present in both the lead frame substrate 10 and the metal coating 20.

(12) To form a package, the substrate 10 is placed in mold 30. The mold is formed of a first piece 32 and a second piece 34. The second major surface 18 of substrate 10 is placed against the second piece 34 of the mold. The first piece 32 is then placed to define a molding cavity 40 between the first piece 32 and the first major surface 16 of the substrate 10, with sidewalls 36 around the molding cavity 40 and with a protection flange 38 extending into the notch 14 of the substrate 10. The protection flange 38 hence extends into the substrate 10 past the metal coating 20 and the contact surface 12. Note that the protection flange 38 abuts the inner edge of the notch 14, the inner edge of the notch being the edge adjacent to the contact surface 12.

(13) There will inevitably be a small gap at the interface 46 between the first piece 32 and the substrate 10 or metal coating 20, but this interface 46 is surrounded by the protection flange 38.

(14) Molding compound is then injected into the molding cavity 40 under a predetermined pressure and temperature and solidified with heat to form package walls 42. Note that the molding compound also fills gaps 26. A cure at a predetermined temperature and time is then carried out. The formed package is then removed from the mold 30 (FIG. 2).

(15) In this state, the package includes the substrate 10 with the package walls 42 having an inner surface 44 extending into notch 14. Note that the metal coating 20 of the device mounting surface 22 and the bond pad 24 is spaced from the inner surface 44 of the package walls 42.

(16) In the embodiment shown, the inner surface 44 is angled at angle between 25 and 90 to the first major surface 16. Acute angles less than 90 can provide benefits in the finished device. In particular, angles of 40 to 70 can increase light output. However, for accomodating the largest devices, an angle of 90 would be appropriate.

(17) The process according to the embodiment of FIGS. 1 and 2 may be compared with a comparative example of FIGS. 5 and 6. The comparative example is the same as the embodiment except that the mold 30 in the comparative example omits the protection flange 38. Accordingly, the same reference numbers are used for like components in the comparative example and the description not repeated.

(18) During the process according to the embodiment of FIGS. 1 and 2, molding compound is impeded or prevented from reaching the contact surface 12 by the protection flange 38 which extends between the molding cavity 40 and the contact surface 12.

(19) In contrast, in the comparative example of FIGS. 5 and 6, even if the first piece 32 of the mold abuts the contact surface 12 or the metal coating 20, there remains a gap at the interface 46 which some molding compound enters under pressure. The molding compound will affect the reflectivity and thermal stability of the finished device.

(20) Accordingly, in the comparative example an extra step is needed, namely a deflash step.

(21) Thus, in the embodiment of FIGS. 1 and 2, the protection flange 38 blocks the interface 46 between the metal coating 22 and the first piece 32 of the mold 30. This impedes the molding compound from entering any gap at this interface 46 which in turn means that there is no need for a deflash step to remove molding compound.

(22) Returning to the first embodiment, the package of FIG. 2 may be used to prepare a packaged device as illustrated in FIG. 3. A device chip 50 is mounted onto the device mounting surface 22 in any known way. If required, bond wires 52 make connection to the bond pads 24 on substrate 10. Alternative bonding techniques such as for example flip chip bonding may also be used. Note that the device mounting surface 22 and bond pads 24 are protected from the intrusion of molding compound in the method of manufacturing the package as discussed above.

(23) Then encapsulant 54, for example of silicone, is introduced into the package between sidewalls 36 of the mold 30 and covering the device chip 50. This encapsulant 54 also fills the empty part of notch 14.

(24) The device chip 50 may in particular be a light emitting diode, LED. The packaged LED device may be used in lighting, for backlight, flash, automotive and display applications, or for traffic signals and the like.

(25) In the embodiment of FIGS. 1 to 3, the inner surface 44 is angled at an acute angle less than 90 to the contact surface which provides an angled reflector for capturing light from the LED device 50 and directing it forwards out of the package.

(26) In an alternative embodiment, illustrated in FIG. 4, the side walls 42 are vertical, i.e. at 90 to the contact surface 12 covered in metal coating 20. In this embodiment, the inner face 44 of the sidewall extends vertically from the edge of the notch 14 adjacent to the contact surface 12. The side wall 42 completely fills the notch.

(27) Although the embodiments above use a lead frame as the substrate 10, the invention may also be applied to other substrate types. In an alternative example, the lead frame is replaced by a flexible substrate having metallisations. Further alternative examples may include the use of an inflexible substrate.

(28) In the case where the substrate is insulating, not a conductive lead frame, it is possible to provide the gaps 26 only in the metallisation 20 and not in the substrate 10.

(29) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.