GB2559146A - Integrated circuit wire formed for welding - Google Patents

Abstract

A process for welding a wire 100 to sheet material 130 of a printed circuit board, where the wire is deformed before welding. The end 102 of the wire 100 may form: a general wedge shape; a flat side 104 which contacts the sheet material during welding; or, a shape which is complimentary to the shape of the sheet material it contacts. A transition area 108 may be formed between the end 102 and a generally round portion 112 of the wire 100, the transition area 108 being modeled based on at least one of: the amount of deformation; an amount of remaining section; and, the stress concentration near the transition area 108. Both the wire 100 and the sheet material 130 may be formed from a range of metals or alloys. The wire 100 may be annealed with heat treatment.

Description

I, EPODOC & TXTA (74) Agent and/or Address for Service:

Wilson Gunn

5th Floor, Blackfriars House, The Parsonage, MANCHESTER, M3 2JA, United Kingdom (54) Title of the Invention: Integrated circuit wire formed for welding

Abstract Title: Deforming the end of a wire before welding to a printed circuit board (57) A process for welding a wire 100 to sheet material 130 of a printed circuit board, where the wire is deformed before welding. The end 102 of the wire 100 may form: a general wedge shape; a flat side 104 which contacts the sheet material during welding; or, a shape which is complimentary to the shape of the sheet material it contacts. A transition area 108 may be formed between the end 102 and a generally round portion 112 of the wire 100, the transition area 108 being modeled based on at least one of: the amount of deformation; an amount of remaining section; and, the stress concentration near the transition area 108. Both the wire 100 and the sheet material 130 may be formed from a range of metals or alloys. The wire 100 may be annealed with heat treatment.

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INTEGRATED CIRCUIT WIRE FORMED FOR WELDING

BACKGROUND OF THE INVENTION

1. Field of the Invention [01] The subject disclosure relates to welding wire on printed pads for connection to integrated circuits and, in particular, an improved wire for use in such a welding process.

2. Background of the Related Art [02] Integrated circuits are ubiquitous in modern devices, appliances, equipment, vehicles and the like. Typically, the integrated circuit package has an electrical printed circuit that requires mechanical and electrical feedthrough to outside connections. To facilitate the connections, the electrical printed circuit will include pads for welding thin wires thereto.

[03] Often the welded connections are covered by fixing layers to increase the mechanical strength of the connection. As a result, when force is applied to the system, the wire may break but not the weld. The maximum pull force of the welded wire connection is limited. In order to obtain a stronger feedthrough, it is helpful to increase the strength of the wire. A stronger wire (e.g., ultimate tensile strength) is generally a harder wire such as measured by Vickers hardness.

Unfortunately, harder wires are much more difficult to weld. Weld strength is also related to electrical conductivity. Thus, it is important to maintain good weld quality even with mechanical fixation by fixing layers.

[04] Referring to Figures 1 and 2, in a typical weld, weld electrodes 10 attach a round wire 12 to a sheet material or flat pad 14 on a substrate 16 (see Figure 2). The contact area is increased by pressing the wire 12 on to the pad 14 during welding such as shown by force arrow “a”. A soft wire and/or significant application of pressure will deform the wire 12 to increase the contact area. In effect, as part of the welding process, a small portion of the wire 12 flattens out to increase the contact area. As shown in Figure 2, the deformation of the wire 12 is irregular. For example, the weld electrodes 10 may leave indentations 18 in the wire 12. The irregularities may cause weak spots that can lead to failure of the connection.

SUMMARY [05] The subject technology provides a process for creating a good weld with harder wire and the components to accomplish the good weld. The subject technology is largely wire hardness independent. Thus, the subject technology can weld any wire on a sheet material, printed electrical pad etc. or other material. The subject technology can provide a wire weld with increased mechanical strength that is designed to remain intact even if the fixation layers fail. The subject technology may also provide enhanced electrical conductivity by increasing the contact area (i.e., increased contact area leads to lower resistance) and/or the quality of the weld.

[06] The subject technology overcomes the problem that the strength of the weld is determined by the size of the contact area formed, which is dependent upon deformation of the wire in the prior art. This problem is particularly acute when welding strong wires (e.g., hard wires) on weak sheet materials because only a limited force can be applied so that limited deformation occurs. As a result, the strength of the weld is limited in the prior art.

The subject technology is particularly suited to welding hard wires to soft sheet material with improved strength and other beneficial qualities.

[07] In one embodiment, the subject technology is directed to a process for welding a wire to sheet material of a printed electrical circuit. The process includes the steps of: deforming an end of the wire before welding; and welding the deformed end to the sheet material. The end may form a general wedge-shape. The process may also include: forming a flat side on the end to create the deformed end; and placing the flat side on the sheet material before welding. In another embodiment, the process includes: forming an end shape on the end to create the deformed end, wherein the shape is complimentary to a sheet material shape of the sheet material; and placing the end shape on the sheet material shape before welding. Preferably, the process forms a transition area between the end and a generally round profde of the wire. The transition area is modeled. Further, the wire may be fabricated from a hard material and the sheet material may be fabricated from a soft material. To make the wire hard, the process may anneal the wire with heat treatment, although in the case of oxide dispersion fortified materials, excessive annealing can be detrimental to desirable wire properties.

[08] The process of the subject technology enables the welding of a hard wire on a weak or weakly supported sheet material. The process is applicable to any kind of material combination and particularly suitable for ceramic oxide dispersion strengthened noble metal composite refractory materials. In one embodiment, the wire and sheet material are fabricated from material selected from the group consisting of silver, copper, gold, lead, tungsten, molybdenum, platinum, ruthenium, rhodium, combinations thereof, and alloys thereof or any other metal, particularly beneficial for dispersion hardened and ceramic/oxide dispersion hardened material.

[09] It should be appreciated that the subject technology can be implemented and utilized in numerous ways, including without limitation as a process, an apparatus, a system, a device, a method for applications now known and later developed. These and other unique features of the system disclosed herein will become more readily apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS [10] So that those having ordinary skill in the art to which the disclosed technology appertains will more readily understand how to make and use the same, reference may be had to the following drawings.

[11] Figure 1 illustrates components for making a prior art weld.

[12] Figure 2 illustrates a prior art weld.

[13] Figure 3 somewhat schematically illustrates components for making a weld in accordance with the subject disclosure.

[14] Figure 4A is a weld in accordance with the subject disclosure.

[15] Figure 4B is a top view of a series of welds in accordance with the subject disclosure.

[16] Figure 5 is a probability plot of force to illustrate the advantages of the subject technology.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [17] The subject technology overcomes many of the prior art problems associated with robust and conductive welds of wires to sheet material. The advantages, and other features of the technology disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain preferred embodiments taken in conjunction with the drawings which set forth representative embodiments of the present technology and wherein like reference numerals identify similar structural elements.

[18] Referring now to the Figure 3, a wire 100 about to be attached to a sheet material 130 by welding electrodes 140 in accordance with the subject disclosure is shown. The wire 100 is deformed before welding. The wire 100 may be ground flat, stamped, pressed, etched, melted and the like to form the desired shape.

[19] In the embodiment of Figure 3, an end 102 of the wire 100 to be welded is flattened into a wedge-shape. The end 102 has opposing flat sides 104 with a sidewall 106 extending therebetween. The sidewall 106 terminates in a flat tip 110 that is substantially perpendicular to the axial length of the wire 100. The flat sides 104 and sidewall 106 form a transition area 108 as the overall wire shape returns to the undeformed round portion 112. In another embodiment, the end 102 tapers more gradually town to the flat tip 110 or even to a pointed/rounded tip.

[20] The transition area 108 is modeled in order not to lose the benefit of using a stronger material for the wire. Preferably, certain conditions are optimized in order to not lose the benefit of the strong wire 100. For example, the following are some conditions to that impact performance: the area of deformation should be kept as small as possible; the section of the wire should be kept as high as possible after the deformation; the deformations themselves should be minimized; transitions should be smooth and gradual; and sharp egdes, corners and any kind of scratches that can act like a stress concentrator are to be avoided. Several desirable shapes are:

flattened at two sides of the wire with a smooth transition from the flat region towards the round region (the walls extending between the flattened sides may maintain the round shape of the wire); flattened at one side of the wire with a smooth transition from the flat region towards the round region (the remaining portion may maintain the generally round shape); and any shape that mimics the surface of the counterpart (e.g., sheet material or contact pad), including a smooth transition to the non-deformed part of the wire.

[21] The flat region improves the weld of a hard wire. Recognizing relative use of the terms hard and soft, it is the strength of the counterpart (e.g., sheet material) that sets the threshold. One can distinguish three working scenarios. The first working scenario is that the required force to deform the wire 100 during welding is larger than the ultimate force that the sheet material 130 can accept. In this first scenario, it is highly desirable that the deformation occurs before the weld process. In the second working scenario, the required force to deform the wire 100 during welding is considerably lower than the ultimate force that the sheet material 130 can accept. In this second scenario, although not required, there is still added value to introducing the extra pre-deformation process step. The prior deformation may help in improving the process reproducibility. The third scenario is that the required force to deform the wire during welding is lower but of the same order as the ultimate force that the sheet material

130 can accept. In this third scenario, it is advised to introduce the flattening as a separate step to make the process robust for all variations and, thus, likely avoiding some low amount of eventual cracking of the sheet material 130 or other portion.

[22] The flat sides 104 create increased surface contact while only needing to apply minimal force, if any, during welding. It is envisioned that the lower flat side 104 is formed to be complimentary to the sheet material 130. Depending upon the technology and application, the lower flat side 104 can take any complimentary shape. For example, in screenprinting, the counter surface varies from flat towards slightly convex or concave. Typically, deposition techniques and other semiconductor processes usually generate flat layers or layers that follow the shape of the substrate. The upper flat side 104 may be formed to be a complimentary shape for interaction with the weld electrodes 140 or left generally round as electrodes 140 are often designed to weld round wires. For example, the electrode tips may be concave to match the round profile of the wire.

[23] Referring now to Figure 4A, a side view of a completed weld 201 in accordance with the subject disclosure is shown. The end 202 of the wire 100 was flattened prior to welding.

As the flat shape is complimentary to the sheet material 130, the welding together of the wire

100 and sheet material 130 is very effective. The sidewall 106 may match and continue the general shape of the round part 112.

[24] Referring now to Figure 4B, a series of completed welds 250 in top view accordance with the subject disclosure are shown. The sheet material 230 and the wire 200 illustrate the welds 250. The wires 200 have opposing flat sides 204. The top sides 204 are easily recognized as the shape is not created by the weld electrodes but rather preformed. The wires 200 have an angled transition area 208 from the flat shape to the undeformed round portion

212. It is envisioned that a working flat does not necessarily need to be a high deformation. The wires 200 may also have indentations 218 from the weld electrodes (not shown). The sheet material 230 may include conductive pads 219 deposited thereon.

[25] Referring now to Figure 5, a probability plot 500 of force is shown to illustrate the advantages of the subject technology. The probability plot 500 has percentage of the population on the vertical axis versus force on the horizontal axis. The distribution of a failure mechanism is usually not a normal distribution but lognormal or Weibull. The probability plot 500 is a representation that allows both plotting the data values and showing the correlation with the fitted lognormal or weibull distribution.

[26] In Figure 5, a legend 502 is included. The legend 502 includes two different studies of a typical reference wire (e.g., “harder oxide-grain-stabilized PT wire” which is wire that has been improved by hardening and “softer oxide-grain-stabilized PT wire”) in contrast with the same type wire improved in accordance with the subject technology (e.g., each flattened approximately 19%). The weld process is with a soft platinum wire. In other words, the required force to deform the wire is considerably lower than the force the counterpart can accept before the counterpart excessively plastically deforms.

[27] The probability plot 500 highlights the improved performance of the subject technology. As can be seen, the wires that are flattened 19% track to the right of the corresponding unflattened wire on the plot 500. In other words, flattening creates a more reliable weld capable of withstanding greater force (e.g., stronger welds). The effect was particularly pronounced with the flattened harder oxide-grain-stabilized PT wires as shown by a best fit or average line 512 for the flattened harder oxide-grain-stabilized PT wire as compared to the best fit or average line 514 for the non-flattened harder oxide-grain-stabilized PT wires. The probability plot 500 also includes a table 503. The table 503 includes parameters 504 relating to the shape and scale of how the wires were deformed, the sample number 506, coefficients 508, and the probability 510.

[28] It will be appreciated by those of ordinary skill in the pertinent art that the functions of several elements may, in alternative embodiments, be carried out by fewer elements, or a single element. Similarly, in some embodiments, any functional element may perform fewer, or different, operations than those described with respect to the illustrated embodiment. Other embodiments may include sheet material and wire ends of various shapes. For example, the wire end and sheet material may form complimentary V-shapes, complimentary convex and concave surfaces, and the like.

[29] Further, although the subject technology has been described with respect to the field of welding wires onto sheet material in an electrical printed circuits, the subject technology is equally applicable to other fields and applications. For example, any wire being attached to anything can benefit from performing the wire to increase the strength of the attachment. For example, the subject technology is also applicable when welding two wires to each other, possibly in a crossed arrangement. It is particularly beneficial when one of the wires is significantly harder than the other.

[30] While the subject technology has been described with respect to preferred embodiments, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the subject technology without departing from the spirit or scope of the invention as defined by the appended claims. For example, each claim may depend from any or all claims in a multiple dependent manner even though such has not been originally claimed.

WHAT S

Claims (11)

CLAIMED IS:

1. A process for welding a wire to sheet material of a printed electrical circuit, the process comprising the steps of:

deforming an end of the wire before welding; and welding the deformed end to the sheet material.

2. A process as recited in Claim 1, wherein the end forms a general wedge-shape.

3. A process as recited in Claim 1, further comprising the steps of: forming a flat side on the end to create the deformed end; and placing the flat side on the sheet material before welding.

4. A process as recited in Claim 1, further comprising the steps of: forming an end shape on the end to create the deformed end, wherein the end shape is complimentary to a sheet material shape of the sheet material; and placing the end shape on the sheet material shape before welding.

5. A process as recited in Claim 1, further comprising the steps of:

forming a transition area between the end and a generally round profde of the wire; and modeling the transition area based on at least one parameter selected from the group consisting of: an amount of deformation; an amount of remaining section; and stress concentration near the transition area from deformed to non-deformed.

6. A process as recited in Claim 1, further comprising the steps of: fabricating the wire from a material selected from the group consisting of silver, copper, gold, lead, tungsten, molybdenum, platinum, ruthenium, rhodium, combinations thereof, and alloys thereof; and fabricating the sheet material from a material selected from the group consisting of silver, copper, gold, lead, tungsten, molybdenum, platinum, ruthenium, rhodium, combinations thereof, and alloys thereof.

7. A process as recited in Claim 1, further comprising the step of annealing the wire with heat treatment.

8. A wire for welding to sheet material of a printed electrical circuit, the wire comprising:

a deformed end of the wire with a general wedge-shape with at least one flat side for placing the flat side on the sheet material before welding; and a transition area between the deformed end and a generally round profile of the wire.

9. A wire as recited in Claim 8, wherein the transition area is modeled based on at least one parameter selected from the group consisting of: an amount of deformation; an amount of remaining section; and stress concentration near the transition area from deformed to nondeformed.

10. A wire as recited in Claim 8, wherein the wire and sheet material are fabricated from material selected from the group consisting of silver, copper, gold, lead, tungsten, molybdenum, platinum, ruthenium, rhodium, combinations thereof, and alloys thereof.

11. A wire as recited in Claim 8, wherein the wire is annealed with heat treatment.

Application No: GB1701313.7 Examiner: Nathan John

Claims searched: 1-11 Date of search: 23 May 2017

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JP H0757790 A (TOKAI RIKA CO) See especially: Abstract;