EP1386345A2

EP1386345A2 - Method for manufacturing a semiconductor device and support plate therefor

Info

Publication number: EP1386345A2
Application number: EP02720409A
Authority: EP
Inventors: Marc A. De Samber; Nicolaas J. A. Van Veen; Johannus W. Weekamp; Erik C. E. Van Grunsven
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2001-04-26
Filing date: 2002-04-22
Publication date: 2004-02-04
Also published as: JP2004520717A; WO2002089184A3; WO2002089184A2

Abstract

The invention relates to a method of manufacturing a semiconductor device (10) comprising a semiconductor element (1), with two or more elements (1) being attached to a support plate (2). It is often desired in such a case that the elements(1) are positioned on the support plate (2) or on a further support plate (22) at a larger mutual distance than in the semiconductor body (100) in which the elements (1) are formed. According to the invention, the support plate (2) is formed as an array of rigid subplates (2A) to which the elements (1) are attached, and the rigid subplates (2A) are interconnected within the plate (2) by means of one or more flexible elements (3). In this way the elements (1) - after they have been attached to the support plate (2) and after they have been separated from each other within the semiconductor body (100) and after stretching of the flexible elements (3) - can be positioned in an accurate manner at a larger mutual distance. Subsequently - or after having been transferred to a further plate (22) - the elements (1) may be provided with an encapsulation (20) and can be mounted on to individual semiconductor devices (10).

Description

Method for manufacturing a semiconductor device, semiconductor device obtained in this way and suitable support plate for this semiconductor device

The invention concerns a method for manufacturing a semiconductor device comprising a semiconductor element, with two or more semiconductor elements being attached to a support plate. The invention also concerns a semiconductor device obtained using such a method and a support plate suitable for use in such a method. Such a method, semiconductor device and support plate are known from

American patent specification US 5.989.982, published on 23 November 1999. This describes how a semiconductor body that comprises individual semiconductor elements, such as diodes, is secured to a support plate, after which the semiconductor body is sawn into parts that each comprise, for example, one semiconductor element, the carrier plate being saved to a large extent at least in said process. Then the sides and (part of) the topside of each semiconductor element are covered - in a suitable device -with a passivating encapsulation. Following removal of each semiconductor element from the support plate, individual semiconductor devices are obtained that are suitable for (further) final assembly. In order to increase the space between the semiconductor elements the (rubber) saw film that functions as a support plate can be stressed after sawing and before providing the encapsulation. As a result, the passivating encapsulation between the individual semiconductor elements becomes thicker and individual and well passivated semiconductor devices can be obtained more readily by means of sawing between neighboring semiconductor elements.

One drawback of the known method is that the support plate is not stretched evenly in all directions so that the thickness of the passivating encapsulation between the elements varies and also the absolute position of each semiconductor element is no longer so accurately defined. As a result further final assembly of individual semiconductor devices becomes more difficult.

Therefore, it is an object of the present invention to provide a method of the kind mentioned in the opening paragraph, in which the stated drawback is completely, or at least partly, overcome and which furthermore is very simple and inexpensive.

This object is achieved, in accordance with the invention by a method of the kind mentioned in the opening paragraph, which is characterized in that the support plate is formed as an array of rigid subplates onto which the semiconductor elements are attached, which subplates are interconnected by means of one or more flexible elements. Thanks to such a design a support plate of sufficient solidity is possible which, for example, does not have to be surrounded by a ring like the known support plate that normally comprises a rubber film. Furthermore, such a support plate enables accurate stretching of the support plate (as a whole) in a more controllable manner, because the support plate only has to be stretched very locally, namely at the position of the flexible elements which - depending on the size of an element - take up only a small part of the surface of the support plate. Because the flexible elements can be shaped in a separate process it is also possible to set the stretching capacity with more accuracy. As a result after stretching of the flexible elements, the semiconductor elements attached to the rigid subplates, are at a more accurately determined distance from each other and at the same time in a more accurately determined position. This increases the consistency of the characteristics of individual semiconductor devices - obtained in this way

- and simplifies the further processing of these.

Thus, in a preferred embodiment, after the semiconductor elements have been attached to the rigid subplates, they are positioned at a greater distance from each other through stretching of the flexible elements. Preferably the elements are stretched to the maximum, which means stretched until the material of the elements and/or the plates offers resistance to further stretching. In this way the stated advantages of a method in accordance with the invention are maximized. Constructions that are suitable for the flexible elements are flat spring or a coil spring constructions. The "springiness" of the flexible elements is important to such an extent that the flexible elements form neither a slack connection between the rigid subplates nor a rigid connection. A flat spring construction has the advantage that this - seen in projection - only has to take up a very small surface area so that the - initial - distance between the semiconductor elements can be particularly small. The flat spring can protrude - upwards or downwards - from the surface of the support plate but can also be folded beneath it in the direction of the surface of the support plate so that the whole is virtually flat. The latter is particularly simply achieved if the flexible elements are embodied so as to be flat coil springs.

The relatively small surface that is necessary - in particular in the abovementioned cases - to form the flexible elements makes it possible to position the semiconductor elements already on the support plate when they are still alongside each other

- whether or not partly separated from each other by means of a saw cut - within a semiconductor body in which they are manufactured. Separating the semiconductor elements by means of sawing can also take place following the mounting of the semiconductor body on the support plate.

Following the stretching of the flexible elements the - then individual - semiconductor elements are provided with a passivating encapsulation. Because the flexible elements, at least after stretching, form relatively large openings in the support plate it is also possible - if desired - to cover the lower side of the semiconductor element (with one of the rigid subplates on this side) with the passivating encapsulation. If the rigid subplates are composed of a(n) (electrically) conductive material, a device - that is not passivated on said side can still be rendered electrically conductive on said side during final assembly, if desired. In a particularly advantageous embodiment the flexible elements also comprise a

(n)(electrically) conductive material which is preferably the same as that from which the rigid subplates are manufactured. In this case, the flexible elements can also serve as electrical connections for the semiconductor elements, even if the lower side of a semiconductor element is provided with a passivating encapsulation. Each rigid subplate and part of the flexible elements attached to it jointly form a so-called lead frame of each semiconductor element or each semiconductor device. Individual semiconductor devices are obtained - following stretching of the flexible elements and following the application of the passivating encapsulation - by separating the flexible elements for example in the middle. This can, for example, also take place by means of sawing or by means of punching. Thus, a method in accordance with the invention does not only have the advantages already set out above, but is furthermore particularly simple and inexpensive.

In a particularly attractive embodiment of a method in accordance with the invention, in succession the semiconductor body is mounted on the plate, the semiconductor body is divided into the semiconductor elements, and the flexible elements are stretched, after which the plate is placed against a further plate and the semiconductor elements are attached to the further plate and said plate is removed again. Thus, the semiconductor elements can be positioned with a larger mutual distance on the further plate in an accurate and direct manner. For the further plate a conventional lead frame can be chosen and the semiconductor elements on this plate can be provided with a passivating encapsulation, after which the final semiconductor devices are formed from this.

The support plate preferably consists of a two-dimensional array of rigid support subplates, the dimensions of which - seen in projection - approximately coincide with the dimensions of a separate semiconductor element, and the flexible elements have dimensions that approximately coincide with the dimensions of a saw cut in the semiconductor body within which the semiconductor elements are formed.

The invention also comprises a semiconductor device that is by means of a method in accordance with the invention and a support plate suitable for use in such a method.

The invention will now be explained in more detail by means of two examples and the drawing, in which

Figure 1 is a schematic, perspective, partly phantom view of a semiconductor device manufactured by means of a method in accordance with the invention, Figures 2 to 5 are schematic, perspective representations of the device in

Figure 1 in successive stages of manufacture, using a first embodiment of a method in accordance with the invention,

Figure 6 is a schematic, perspective representation of a detail of the device in Figure 1 in a stage of manufacture corresponding to Figures 2 to 4, and Figures 7 to 10 are schematic top views or cross-sectional views of the device in Figure 1 in successive stages of manufacture, using a second embodiment of a method in accordance with the invention.

The figures are not drawn to scale and some of the dimensions are exaggerated for the sake of clarity. Corresponding areas or components are given the same reference numbers whenever possible.

Figure 1 is a schematic, perspective, partly phantom view of a semiconductor device manufactured by means of a method in accordance with the invention. The device 10 comprises a semiconductor element 1 surrounded by a passivating encapsulation 20 of a plastic often used for this purpose, such as an epoxy material. Around the encapsulation 20 there are a number of flexible elements 3 which, within the encapsulation 20, are connected with a subplate 2B - as shown around the device 10 - that is positioned under element 1. By cutting the elements 3, a separate device 10 is obtained. One or more of the elements 3 also already comprise an interrupt within the encapsulation 20 and the part of said interrupt protruding from the encapsulation 20 can - within the encapsulation and behind the interrupt - be connected via a wire 21 with the element 1. In this example both the plates 20 and the elements 3 and the wire 21 are made from an electrically conductive material such as copper or gold. If the element 1 is a diode - as in this example - a flexible element 3 connects the bottomside of the diode 1 with the outside world, and another element 3 that comprises the interrupt bridged by the wire 21 connects the upperside of diode 1 with the outside world. Figures 2 to 5 illustrate in a schematic and perspective manner the device shown in Figure 1 in successive stages of manufacture, using of a first embodiment of a method in accordance with the invention; Figure 6 illustrates in a schematic and perspective manner a detail of the device shown in Figure 1 in a stage of manufacture corresponding to Figures 2 to 4. As shown in Figure 2, a rigid metal plate 2 is employed, here made from copper in a thickness of a few tenths of one millimeter, in which openings 4 are formed by means of lithography and etching, in this example 4 larger openings 4A and four smaller openings 4B between which - in this example - 4 islands 2A are formed. The rigid islands 2A are connected here with the adjoining sections of the rigid plate 2 by flexible elements 3, in this example formed by a meandering section 3 of the plate 2 the construction of which corresponds to that of a flat spiral spring 3, which is shown enlarged in Figure 6. The flexible elements 3 and the openings 4 (4A, 4B) are formed simultaneously in this example by means of lithography and etching. In this example the dimensions of element 1 are 0.3 mm x 0.3 mm and a rigid subplate 2A has roughly the same dimensions. The length of the meandering section thus is likewise 0.3 mm. The thickness of the plate 2 and the flexible elements 3 is 20μm, the same as the width of a flexible element 3 and the width of the opening between two turns of the spiral 3. The numbers of turns is in this example, two which means that the maximum stretch has a length of 0.6 mm. Thus, the total width of the spiral 3 is - in this example - (2 + 3) x 20μm or 100 μm. This roughly corresponds to the width of a saw cut in the semiconductor body 100 that is necessary in order to separate the elements 1 from each other.

Then - see Figure 3 - on each of the four rigid subplates 2A a small area of solder paste is applied. After this - see Figure 5 - a semiconductor body 100 is provided which comprises 4 semiconductor elements 1, in this case diodes 1, that are attached to the plate 2 by means of the solder areas 6. Next the individual elements 1 are separated from each other by channels 41 that are formed by means of sawing or etching. Then - see also Figure 5 - the edges of the plate 2 are pulled apart, causing the flexible elements to be stretched and the mutual distance between the rigid subplates 2A with the elements 1 on top of them to be increased in a regular manner. Following removal - for example by means of sawing - of the edges of the plate 2, a situation corresponding to Figure 5 results. Next - and this is not shown in Figure 5 - for each of the elements 1, one of the flexible elements 3 is cut close to the relevant element 1. The outermost part of the cut flexible element 3 is then connected by means of a wire connection to the upperside of element 1, which is shown in figure 1, not in Figure 5. Thus, both the bottomside and the topside of each element 1 are connected in an electrically conductive manner to a flexible element 3, which electrical connections are electrically insulated from each other.

Then - see Figure 1 - the elements 1, are each surrounded by an insulating encapsulation 20, for example by molding. Then the flexible elements 3 are cut and the device is ready for final assembly.

Figures 7 to 10 are schematic plan views or - like in Figure 10 - a cross- sectional view of, the device shown in Figure 1 in successive stages of manufacture, using a second embodiment of a method in accordance with the invention. In Figure 7, like in the previous example, use is made of a copper plate 2 in which square openings 4, in this example nine of them, are formed by, for example, etching. Between the 9 openings 4 are four rigid subplates 2A to be formed that are surrounded by flexible elements 3 that in this example are constructed so as to be a leaf spring 3. By folding the plate 2, causing two neighboring folding lines 17 to be moved towards each other and the intermediate folding line to be moved downwards, the flexible elements are folded up. In this way - see Figure 9 - the four subplates 2A come to join each other approximately. In this example, an area of glue 66 is then applied to subplates 2A after which - as in the previous example - a semiconductor body 100 with four semiconductor elements is attached to the plate 2. After the semiconductor body has been divided into four individual semiconductor elements 1 in the same way as in the previous example, the plate 2 is unfolded or stretched again until a configuration that is comparable to that of Figure 8 is obtained. In this way, the interspace between the semiconductor elements 1 that in the meantime have been separated from each other is much larger than within the semiconductor body 100. In this example, the plate 2 is then - see Figure 10 - inverted and pressed against a further plate 22 on which solder areas 6 have been provided and on which the actual final assembly of the semiconductor elements 1 takes place. The further plate 22 comprises in this example a conventional lead frame 22 that is suitable for forming four semiconductor devices 10. After the semiconductor elements 1 have been soldered on the further plate 22, the plate 2 is removed. The final semiconductor devices 10 are then obtained from the further plate 22 provided with the semiconductor elements 1 in a manner that has been discussed above in the first example.

The dimensions of the rigid subplates 2A, the flexible elements 3 and the elements 1 are approximately the same in the second example as those in the first example. All this implies that the dimensions of the leaf spring 3 are approximately 0.3 x 0.3 mm. The width of the leaf spring 3 is - in the folded condition - approximately 40 μm and thus allows a smaller of the saw width in the semiconductor body 100 than in the first example.

The invention is not limited to the examples given, and within the scope of the invention many modifications and variations are possible to those skilled in the art. For example, thicknesses and materials can be used that differ from those mentioned in the examples. The invention is particularly suited for the manufacture of a semiconductor device that has a (semi-) discrete semiconductor element such as a diode or a transistor, but can also advantageously be used in the manufacture of ICs.

It is also noted that the method of the first example can also be applied in the manner described in the second example. This means that the semiconductor elements, instead of being soldered, are glued to the plate and once the plate has been stretched the semiconductor elements are attached to a further plate, for example by soldering, after which the plate is removed and the manufacture of the semiconductor device continues on the further plate. It is also noted that although in both examples use is made of a two- dimensional array of subplates, the invention can also be advantageously applied in a one- dimensional manner in which a row of semiconductor devices are formed next to each other. Naturally, in all cases a number of semiconductor devices can be formed that differ from the number selected in the example. Finally, it is noted that apart from a symmetrical, in this case square, geometry of the subplates, a less symmetrical geometry, such as a rectangle, can also be advantageously used, for example, if the elements also have a rectangular shape.

Claims

CLAIMS:

1. Method of manufacturing a semiconductor device (10) comprising a semiconductor element (1), with two or more semiconductor elements (2) being attached to a support plate (2), characterized in that the support plate (2) is formed as an array of rigid subplates (2A) on to which the semiconductor elements (1) are attached, which subplates are interconnected by means of one or more flexible elements (3).

2. Method as claimed in claim 1, characterized in that after the semiconductor elements (1) are attached to the rigid subplates (2A), the rigid subplates (2 A) are positioned at a larger mutual distance by stretching the flexible elements (3).

3. Method as claimed in claim 1 or 2, characterized in that the flexible elements are stretched to the maximum.

4. Method as claimed in claim 1 , 2 or 3, characterized in that for the flexible elements (3), the construction of a, for example flat, helical spring (3) is chosen.

5. Method as claimed in claim 1, 2 or 3, characterized in that for the flexible elements (3) the construction of a flat spring (3) is chosen.

6. Method as claimed in any one of the preceding claims, characterized in that the support plate (2) is formed as a two-dimensional array of rigid subplates (2) that are interconnected in two mutually perpendicular directions by the flexible elements (3).

7. Method as claimed in any one of the preceding claims, characterized in that the semiconductor elements (1) are manufactured within a semiconductor body (100) and the semiconductor body (100) before stretching of the flexible elements (3), is attached to the support plate (2), and the semiconductor elements (1) are at least largely separated from each other before or after the semiconductor body (100) is provided on the carrier plate 2.

8. Method as claimed in any one of the preceding claims, characterized in that after the semiconductor elements (1) are attached to the subplates (2 A) and after stretching of the flexible elements (3), the semiconductor elements (1) are provided with a passivating encapsulation (20) after which the semiconductor elements (1) provided with the encapsulation (20) are separated from each other by partitioning of the flexible elements (3).

9. Method as claimed in any one of the preceding claims, characterized in that from the rigid subplates (2A) and the flexible elements (3) so-called lead frames for the semiconductor elements (1) are formed.

10. Method as claimed in any one of claims 1 to 7, characterized in that after the semiconductor body (100) is provided on the plate (2) and following the division of the semiconductor body (100) into the semiconductor elements (1) and following stretching of the flexible elements (3), the plate (2) is placed against a further plate (22) and the semiconductors elements (1 ) are attached to the further plate (22), after which the plate (2) is removed.

11. Method as claimed in claim 10, characterized in that for the further plate (22) a lead frame (22) is chosen, and the semiconductor elements (1) on the further plate (22) are provided with a passivating encapsulation (20) after which the semiconductor devices (10) are formed from this.

12. Semiconductor device (10) comprising a semiconductor element (1) manufactured by means of a method as claimed in any one of the preceding claims.

13. Support plate (2) for use in a method as claimed in any one of claims 1 to 11, characterized in that the carrier plate (2) comprises an array of two or more rigid subplates (2 A) that are interconnected by means of one or more flexible elements (3).