A LEAD FRAME FOR AN OPTO-COUPLER

Abstract: A lead frame (2) for manufacturing an opto-coupler (1) includes an emitter portion (3), a detector portion (4), a first contact portion (5) and a second contact portion (6). Each of the portions (3-6) are adjacent to but spaced from each of the other portions (3-6). A mold cavity (7) encircles the portions (3-6) and extends below the portions (3-6) but not across the upper surface of the portions (3-6). The mold cavity (7) is molded from an electrically insulating material.

Description: A Lead Frame for an Opto-Coupler The invention relates to a lead frame for an opto-coupler and a method of manufacturing an opto-coupler. Generally, there are two different designs that are commonly used to manufacture opto-couplers. These are: (i) the over-under design; and (ii) the coplanar design. (i) In the "over-under" design concept, separate lead frames are used for the emitter and the detector. The emitter and detector lead-frames are then positioned with one above the other and coupled together. As a result, the emitter and detector are "over-under" each other and the gap between the emitter and the detector provides the electrical isolation. An inner translucent material is then molded around the emitter and detector to provide the optical coupling between the emitter and the detector. Subsequently, a dark outer molding is used to encapsulate and protect the whole package. One of the main advantages of this design is the good electrical isolation provided by the gap between the emitter and the detector. However the "over-under" coupling process itself hinders manufacturing flexibility as it involves processing and greater care is required during the coupling process. (ii) In the coplanar design, both the emitter and detector chips are bonded on the same plane. These are then encased in a "blob" of translucent resin in order to provide the optical coupling. The whole structure is then encapsulated to protect the package from the environment. This design has the advantage that it is easier to manufacture compared to the "over- under" design, as the manufacturing process is simplified due to its similarity to current conventional back-end processes. However, a major weakness of this design is the lower electrical isolation capability. This is due to the use of a "blob" of molding material to surround the emitter and detector, as this limits the physical separation (and therefore, electrical isolation) of the emitter and detector. In accordance with a first aspect of the present invention, a lead frame for manufacturing an opto-coupler comprises an emitter portion, a detector portion, a first contact portion and a second contact portion, each of the portions being adjacent to but spaced from each of the other portions; and a mold cavity encircling the portions and extending below the portions but not across the upper surface of the portions, and the mold cavity being molded from an electrically insulating material. In accordance with a second aspect of the present invention, a method of manufacturing an opto-coupler comprises providing a lead frame in accordance with the first aspect of the invention, attaching an optical radiation emitter device to the emitter portion, attaching an optical radiation detection device to the detector portion, bonding a first electrically conducting wire between a contact surface on the emitter device and the first contact portion, bonding a second electrically conducting wire between a contact surface on the detector device and the second contact portion; introducing a first molding material into the mold cavity and curing the molding material, the first molding material transmitting optical radiation when cured; and covering the exposed surface of the first molding material with a second molding material that is opaque when cured. The term "optical radiation" as used herein means radiation in the ultra-violet, visible or infrared regions of the electro-magnetic spectrum. Preferably, the portions on the lead frame are coplanar with each other. Preferably, the mold cavity is formed on the lead frame by a molding process, such as an injection molding process. Typically, the mold cavity is formed from material that has a light colour, and preferably, is substantially white when cured. Preferably, the second molding material has a light colour, and preferably, is substantially white when cured. Preferably, method further comprises, after permitting the second molding material to cure, encapsulate mold cavity and the second molding material in the third molding material. An example of a lead frame for an opto-coupler and a method of manufacturing an opto-coupler in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a plan view of a lead frame having an opto-coupler formed thereon, prior to singulation; Figure 2 is a cross-sectional view of the opto-coupler of figure 1 along the line AA; and Figure 3 is a cross-sectional view of the opto-coupler along the line BB. Figure 1 is a plan view of an opto-coupler 1 manufactured on a lead frame 2. Figure 1 shows only a portion of the lead frame 2. Typically, the lead frame 2 would be a straight lead frame or a matrix lead frame that would have a number of opto-couplers 1 manufactured on it. The opto-couplers 1 would then be separated from each other in a process known as "singulation". The lead frame 2 includes, for each opto-coupler 1 , an emitter portion 3, a detector portion 4, an emitter contact portion 5 and a detector contact portion 6. Each of the portions 3-6 are encircled by a mold cavity 7, which also electronically insulates each of the portions 3-6 from each other, as shown in Figures 2 and 3. During manufacturing, the lead frame 2 is supplied with the mold cavity 7 premolded onto the lead frame 2. For example, the mold cavity 7 may be premolded onto the lead frame 2 by a conventional injection molding process. In addition, preferably, the mold cavity 7 is formed from a white molding material. It will also be noted that the mold cavity 7 extends below the portions 3-6 but does not extend across the upper surfaces of the portions 3-6. To manufacture the opto-coupler 1 , the lead frame 2 with the premolded cavity 7 is taken and an emitter 8 is attached to the emitter portion 3 and a detector 9 is attached to the detector portion 4. A wire bond 10 is then formed between the emitter 8 and the emitter contact portion 5, and another wire bond 11 formed between the detector 9 and the detector contact portion 6. After the wire bonds 10, 11 have been formed, the mold cavity is filled with a translucent mold material 12 which covers the top surfaces of the portions 3-6, the emitter 8, the detector 9, and the wire bonds 11 , 12. After the translucent molding material 12 has cured, an opaque white layer 13 of molding material is applied over the exposed surface of the translucent mold material 12. After the layer 13 has cured, the mold cavity 7 and the white opaque layer 13 are encapsulated in an outer protective molding material 14. After singulation, the only sections of the lead frame 2 extending from the outer mold material 14 are sections 3a, 4a, 5a, 6a of the lead frame 2 which form the electrical contact pins for the opto-coupler 1. Advantages of the invention are that it does not have the handling problems associated with the "over under" design, and by providing a pre-formed mold cavity 7 on the lead frame 2, it is possible to manufacture an opto-coupler 1 with electrical isolation between the portions 3-6 which is greater than for conventional coplanar designs. Furthermore, there is an advantage that manufacturing of the opto-coupler 1 can be performed using the "reel to reel" process. This has the advantage of enhancing manufacturing efficiency and reducing time loss due to operator handling.

Claims: CLAIMS 1. A lead frame for manufacturing an opto-coupler comprising an emitter portion, a detector portion, a first contact portion and a second contact portion, each of the portions being adjacent to but spaced from each of the other portions; and a mold cavity encircling the portions and extending below the portions but not across the upper surface of the portions, and the mold cavity being molded from an electrically insulating material. 2. A lead frame according to claim 1 , wherein the portions on the lead frame are coplanar with each other. 3. A lead frame according to claim 1 or claim2, wherein the mold cavity is formed on the lead frame by a molding process, such as an injection molding process. 4. A lead frame according to any of the preceding claims, wherein the mold cavity is formed from material that is substantially white. 5. A method of manufacturing an opto-coupler, the method comprising providing a lead frame in accordance with any of the preceding claims, attaching an optical radiation emitter device to the emitter portion, attaching an optical radiation detection device to the detector portion, bonding a first electrically conducting wire between a contact surface on the emitter device and the first contact portion, bonding a second electrically conducting wire between a contact surface on the detector device and the second contact portion; introducing a first molding material into the mold cavity and curing the molding material, the first molding material transmitting optical radiation when cured; and covering the exposed surface of the first molding material with a second molding material that is opaque when cured. 6. A method according to claim 5, wherein the second molding material is substantially white when cured. 7. A method according to claim 5 or claim 6, further comprising, after permitting the second molding material to cure, encapsulating mold cavity and the second molding material in a third molding material.

Inventors: CHUA CHEE SEONG, LOW TEK BENG, CHUA, CHEE, SEONG, LOW, TEK, BENG
Applicants: CHUA CHEE SEONG, INFINEON TECHNOLOGIES AG, LOW TEK BENG, CHUA, CHEE, SEONG, LOW, TEK, BENG
Application year: 2001
Main classification: H01L31
IPC codes: H01L31