Yeow, How Mong (7 Pemimpin Drive, #09-06, Singapore 0, 57615, SG)
Kee, Bee Ngoh (290 Bukit Batok Street 24, #16-105, Singapore 0, 65529, SG)
Yeow, How Mong (7 Pemimpin Drive, #09-06, Singapore 0, 57615, SG)
Kee, Bee Ngoh (290 Bukit Batok Street 24, #16-105, Singapore 0, 65529, SG)
| 1. | A method of forming an integrated circuit package including: locating an integrated circuit in relation to a leadframe ; forming wires between electrical contacts of the integrated circuit and leads of the leadframe, the wires being inserted into recessed portions of the respective leads, and encapsulating the integrated circuit, wires and the electrical connections between the wires and the leads in a resin body. |
| 2. | A method according to claim 1 in which the step of forming the wires includes: (i) bonding the wires to the contacts of the integrated circuit; (ii) inserting a portion of the wire into the recessed portion of the lead ; and (iii) bonding another portion of the wires to the leads. |
| 3. | A method according to claim 1 in which the step of forming the wires includes: (i) bonding a portion of the wires to the leads ; (ii) inserting another portion of the wire into the recessed portion of the lead ; and (iii) bonding the wires to the contacts of the integrated circuit;. |
| 4. | A method according to any of claims 1 to 3 in which the recessed portion of the lead is slightly narrower than the diameter of the wire, and the wire is forced into the recessed portion with sufficient force that it is slightly deformed. |
| 5. | A method according to any preceding claim in which the wires are formed flexing in a given direction away from the lead frame, and the recessed portion of the lead frame is displaced in the same direction from the plane in which the wires are bonded to the lead frame. |
| 6. | An integrated circuit package including : an integrated circuit; a resin body; leads extending out of the resin body; and wires encapsulated in the resin body and electrically connecting electrical contacts of the integrated circuit to respective ones of the leads, wherein the leads include a recessed portion and the wires are inserted into recessed portions of the respective leads. |
| 7. | An integrated circuit according to claim 6 in which the recessed portion of the lead is slightly narrower than the diameter of the wire, and the portion of the wire within the recessed portion is slightly deformed. |
| 8. | An integrated circuit according to claim 6 or claim 7 in which the wires flex in a given direction away from the leads and integrated circuit, and the recessed portion of the leads is displaced in the same direction from the plane in which the wires are bonded to the leads. |
Background of Invention The term"integrated circuits"is used in this document refers to dies, usually consisting substantially of semiconductor material, having electrical contacts formed in their upper surface. During the packaging process, the dies are embedded in a resin body from which extend electrically conductive leads, in electrical contact with the contacts of the integrated circuit.
The most common packaging method is illustrated in Fig. 1. The integrated circuit 1 is positioned on a die pad 3 of a lead frame. The lead frame further includes leads 5 extending inwardly towards the die. Wires 7, typically of aluminium, are formed between respective ones of the contacts 9 of the die and the leads 5. The wires 7 are typically bonded to the contacts 9 and leads 5 at respective connection points 11,13 by a mechanism such as ultrasonic transmission, in which an intermetallic layer is formed between the leads 5 and the aluminium wires 7, providing a certain level of adhesive strength.
Subsequently, a resin body is moulded around the wire bonds, enclosing the integrated circuits, the wires 7 and the tips of the leads 5 including the connection points 13. The leads 5 are then cut at a location which is outside the resin body, leaving a portion of them extending from the resin body, to complete the packaging process.
This packaging technique, though very common, suffers from the disadvantage that when the package is subject to a high stress the wires 7 may lift off the leads 5 at the connection points 13. In particular, delamination at the interface of the mold compound and the leads 5 propagates towards the connection point 13 between the wires 7 and the leads 5, and the wires may be torn off the leads. Only the adhesion strength of the metallic interface between the lead 5 and wires 7 prevents this happening, and frequently this adhesion strength is inadequate. Techniques have been proposed to increase the adhesion strength, but these techniques can only increase the adhesion strength to a limited degree, and they cannot totally eliminate the problem.
Summary of the Invention The present invention aims to provide new and useful techniques for packaging integrated circuits, and new and useful packaged integrated circuits. In particular, the invention aims to provide integrated circuit packages in which the wires are less liable to lose electrical contact with the leads.
In general terms, the invention proposes that the leads are formed with a recessed portion for receiving a portion of the wire. Thus, the wire makes contact with the lead in the recessed portion, and when the wire is encased in the resin it is held firmly there. Accordingly, the resin holds the wire and lead in contact. Thus, there is a substantially fail-proof connection between the contacts of the integrated circuit and the leads.
Preferably, the recessed portion of the lead is slightly narrower than the diameter of the wire, and the wire is forced into the recessed portion with sufficient force that it is slightly deformed. Thus, the wire is held in the recessed portion by mechanical (frictional) force between the sides of the recessed portion and the wire.
Preferably, as in existing systems, the wire extends also to a planar surface of the lead, where a wire bond is formed between the lead and the wire. Thus, the portion of the wire which is received in the recessed portion of the lead may be between the two ends of the wire, which are respectively bonded to the corresponding contact of the die and the corresponding lead.
Typically, the order of the steps in the wire bonding is (i) that the wire is bonded to either the contact or the lead (it may be either one), (ii) that a central portion of the wire is inserted into the recessed portion of the lead, and (iii) that the wire is bonded to the other one of the contact and the lead.
In arrangements in which the wires flex in a given direction away from the lead frame, then the recessed portion of the leads is preferably displaced in the same direction from the plane in which the wires are bonded to the leads.
For example, in many conventional arrangements, the wires flex"upwards" (i. e. in the direction from the die pad towards the integrated circuit), and in this case preferably the leads include a raised section which is above the plane of the lead frame where the wires are bonded to the leads, and the recessed portions of the leads are in these raised sections of the leads.
Specifically, a first expression of the invention is a method of forming an integrated circuit package including: locating an integrated circuit in relation to a leadframe ; forming wires between electrical contacts of the integrated circuit and leads of the leadframe, the wires being inserted into recessed portions of the respective leads, and encapsulating the integrated circuit, wires and the electrical connections between the wires and the leads in a resin body.
A second expression of the method is an integrated circuit package including : an integrated circuit; a resin body; leads extending out of the resin body; and wires encapsulated in the resin body and electrically connecting electrical contacts of the integrated circuit to respective ones of the leads, wherein the leads include a recessed portion and the wires are inserted into recessed portions of the respective leads.
Brief Description of The Figures Preferred features of the invention will now be described, for the sake of illustration only, with reference to the following figures in which: Fig. 1 is a perspective view illustrating a known packaging method; and Fig. 2 is a perspective view illustrating a packaging method which is an embodiment of the invention; Fig. 3 is a cross sectional view of a part of the structure shown in Fig.
2; and Fig. 4, which is composed of Figs. 4 (a) and 4 (b), illustrates two possible orders of the steps the method of Fig. 2.
Detailed Description of the embodiments Referring to Fig. 2, an embodiment of the invention is illustrated. Elements of Fig. 2 which correspond to those of Fig. 1 are labelled by the same reference numerals. Fig. 2 illustrates a moment in the packaging procedure in which some, but not all, of the wires 7 have been formed.
As in Fig. 1, the wires 7 are bonded at their ends to respective contacts 9 and leads 5. However, in contrast to Fig. 1, in Fig. 2 each of the leads 5 includes a raised end section 15, which includes a recessed portion 17. A central portion of each of the wires 7 is inserted into the recessed portion 17 of the corresponding lead. The depth of the recess is selected according to the diameter of the wire, and may be at least twice the diameter of the wire, such as 2.5 times the diameter of the wire.
Note that, as shown Fig. 1, the wires flex upwardly between the connection positions 11,13. Accordingly, the recessed portions 17 of the leads 5 are also above the horizontal plane containing the connection positions 13, i. e. the part of the recesses where the wires 7 are secured is above the plane of the contact positions 13.
Fig. 3 is a cross-sectional view of a recessed portion 17 in the line A-A shown in Fig. 2, with a wire 7 inside it shown in cross-section. The recess 19 in the recessed portion 17 is of gradually narrowing width towards its base, which is narrower than the undeformed diameter of the wire 7, so that as the central portion of the wire 7 is inserted into the recess 19 it is slightly compressed at its sides, thus ensuring that it is firmly secured.
When all the wires 7 have been formed, the integrated circuit 1, wires 7 and the part of leads 5 including the connection points 11,13, the raised end sections 15 and the recessed portions 17, are fully encased in resin in a mould, to form a resin body (not shown), as in known packaging techniques.
The leads 5 can then be cut, normally leaving a portion of them extending out of the resin body. Thus, the package is completed.
Even if, when the package is in use, a force on the package causes the resin to delaminate from the lead, or even forces the contact 13 between the wire 7 and the lead 5 to be torn apart, the electrical contact between the wire 7 and the recessed portion 17 is ensured by the resin body which completely encapsulates the recessed portion 17 and the wire 7.
Fig. 4 (a) shows the steps of a first method of forming each wire 7 in the embodiment. In step 21, the wire 7 is bonded (e. g. ultrasonically) to the contacts 9 of the integrated circuit 1 ("IC") at the connection point 11. In step 22, a portion of the wire 7 is pushed into the recess of the recessed portion 17. In step 23, the wire 7 is bonded (e. g. ultrasonically) to the lead 5 at the connection point 13.
Fig. 4 (b) shows the steps of a second method of forming each wire 7 in the embodiment. In step 31, the wire 7 is bonded (e. g. ultrasonically) to the lead 5 at the connection point 13. In step 32, a portion of the wire 7 is pushed into the recess of the recessed portion 17. In step 33, the wire 7 is bonded (e. g. ultrasonically) to the contact 9 at the connection point 11.
Note that in either case the wire is formed using conventional equipment, for example a capillary tube through which the wire is gradually dispensed during the three stages of the operation, the final stage including cutting the wire.
Although only a single embodiment of the invention has been described in detail, many variations of the embodiment are possible within the scope of the invention as will be clear to a skilled reader. In particular, many variants of the wire bonding technique illustrated schematically in Fig. 1 are known, and the principles of the present invention are straightforwardly applicable to many of them.