WO2022072254A2

WO2022072254A2 - Interposers for splicing flexible circuits to printed circuit boards

Info

Publication number: WO2022072254A2
Application number: PCT/US2021/052110
Authority: WO
Inventors: Michael Peter Ciaccio
Original assignee: Gentherm Gmbh
Priority date: 2020-09-30
Filing date: 2021-09-27
Publication date: 2022-04-07
Also published as: WO2022072254A3

Abstract

A flexible circuit includes a laminated substrate. The laminated substrate includes a support layer and a conductive layer made of a first metallic material arranged on the support layer. The conductive layer includes conductive traces of the first metallic material. The laminated substrate comprises a layer of a pretreatment coating deposited on the conductive traces. The flexible circuit comprises a component made of a second metallic material soldered to the conductive traces. The soldering sublimates the pretreatment coating.

Description

INTERPOSERS FOR SPLICING FLEXIBLE CIRCUITS TO PRINTED CIRCUIT

BOARDS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No.63/085, 505, filed on September 30, 2020. The entire disclosure of the application referenced above is incorporated herein by reference.

FIELD

[0002] The present disclosure relates generally to flexible circuits and more particularly to intermediate circuits (also called interposers) for splicing flexible circuits to printed circuit boards.

BACKGROUND

[0003] The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] Wiring harnesses are used to connect electrical components in many applications. When a significant number of components need to be connected in a given location, a plurality of wires, printed circuit boards (PCBs), and/or flexible substrates with conductive traces may be used. Typically, the flexible substrates include a single conductive layer and an outer insulating layer (called flexible foil). The single conductive layer may be patterned to define traces, fingers, and other structures that can be used to provide multiple connections.

SUMMARY

[0005] A flexible circuit comprises a laminated substrate. The laminated substrate comprises a support layer and a conductive layer made of a first metallic material arranged on the support layer. The conductive layer includes conductive traces of the first metallic material. The laminated substrate comprises a layer of a pretreatment coating deposited on the conductive traces. The flexible circuit comprises a component made of a second metallic material soldered to the conductive traces. The soldering sublimates the pretreatment coating.

[0006] In another feature, the first metallic material includes aluminum and the second metallic material includes copper.

[0007] In another feature, the first and second metallic materials include aluminum.

[0008] In another feature, the component comprises a second laminated substrate. The second laminated substrate comprises a second support layer and a second conductive layer made of the second metallic material arranged on the second support layer. The second conductive layer includes second conductive traces of the second metallic material that are respectively soldered to the conductive traces of the laminated substrate.

[0009] In another feature, the flexible circuit further comprises a plurality of terminals of a connector that are made of the second metallic material and that are soldered respectively to the second conductive traces on opposite ends relative to the conductive traces.

[0010] In another feature, the flexible circuit further comprises the connector, and the plurality of terminals is inserted into the connector.

[0011] In another feature, the flexible circuit further comprises a dual in line connector including pins made of the second metallic material soldered respectively to the second conductive traces on opposite ends relative to the conductive traces.

[0012] In another feature, the pins are vertical.

[0013] In another feature, the pins are right-angled.

[0014] In another feature, the component comprises a plurality of terminals of a connector respectively soldered to the conductive traces.

[0015] In another feature, the flexible circuit further comprises the connector, and the plurality of terminals is inserted into the connector.

[0016] In another feature, the component includes a printed circuit board (PCB) comprising a second support layer and a second conductive layer made of the second metallic material arranged on the second support layer. The second conductive layer includes second conductive traces of the second metallic material that are respectively soldered to the conductive traces of the laminated substrate. [0017] In other features, the conductive traces are connected in series to form a loop having a first end a second end. The component comprises a first wire soldered to the first end of the loop and a second wire soldered to the second end of the loop.

[0018] In another feature, the flexible circuit further comprises a connector, and distal ends of the first and second wires are connected to the connector.

[0019] In other features, the conductive traces are connected to form N separate loops, where N is an integer greater than 1 . Each of the N loops have a first end a second end. The component comprises N pairs of wires. A first wire in the Nth pair of wires is soldered to the first end of the Nth loop. A second wire in the Nth pair of wires is soldered to the second end of the Nth loop.

[0020] In another feature, the flexible circuit further comprises a connector, and distal ends of the N pairs of wires are connected to the connector.

[0021] In another feature, the laminated substrate is dry milled to form the conductive traces, and edges of the conductive traces taper outwardly and towards the support layer.

[0022] In other features, the flexible circuit further comprises an adhesive layer disposed between the conductive layer and the support layer. The laminated substrate is dry milled to form the conductive traces. Edges of the conductive traces and the adhesive layer taper outwardly and towards the support layer. The edges of the adhesive layer are aligned with the edges of the conductive traces.

[0023] In another feature, the support layer includes a material selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI).

[0024] In another feature, the flexible circuit further comprises a cover layer covering the conductive traces. The cover layer includes a material selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI).

[0025] Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0027] FIG. 1 is a side cross-sectional view of an example of a laminated substrate including a conductive layer, an adhesive layer, and a support layer;

[0028] FIG. 2 is a side cross-sectional view of an example of the laminated substrate of FIG. 1 with dry milled conductive traces;

[0029] FIG. 3 is a side cross-sectional view of an example of the laminated substrate of FIG. 2 with a pretreatment coating applied to the conductive traces;

[0030] FIG. 4 is a side cross-sectional view of an example of the laminated substrate of FIG. 3 with a solder material deposited on the pretreatment coating;

[0031] FIG. 5 shows a side cross-sectional view of a flexible circuit formed using the laminated substrate of FIG. 3 and including aluminum traces that are connected to copper terminals of a connector via a flexible circuit including copper traces;

[0032] FIG. 6 shows a side cross-sectional view of a flexible circuit formed using the laminated substrate of FIG. 3 and including aluminum traces that are connected to vertical copper pins of a header via a flexible circuit including copper traces;

[0033] FIG. 7 shows a side cross-sectional view of a flexible circuit formed using the laminated substrate of FIG. 3 and including aluminum traces that are connected to right angled copper pins of a header via a flexible circuit including copper traces;

[0034] FIG. 8 shows a side cross-sectional view of a flexible circuit formed using the laminated substrate of FIG. 3 and including aluminum traces that are directly connected to copper terminals of a connector;

[0035] FIGS. 9A-9D show a flexible circuit formed using the laminated substrate of FIG. 3 and including aluminum traces that are directly connected to copper traces on a printed circuit board (PCB);

[0036] FIGS. 10A and 10B show examples of a flexible circuit formed using the laminated substrate of FIG. 3 and including one or more aluminum traces used to form one or more flexible heaters; and

[0037] FIGS. 11 and 12 show side cross-sectional views of a conductive trace formed by a mechanical process such as dry milling. [0038] In the drawings, reference numbers may be reused to identify similar and/or identical elements.

DETAILED DESCRIPTION

[0039] Printed circuit boards (PCB’s) are often connected to each other and to other assemblies using wiring harnesses that have connectors on either ends. For example, a first end of a wire harness may have a first connector that plugs into a corresponding connector on a first PCB, and a second end of the wire harness may have a second connector that plugs into a corresponding connector on a second PCB. The wiring harnesses and associated connectors not only add cost and occupy space but can also develop contact problems and issues such as bent or broken connector pins over time.

[0040] Flexible circuits can replace wiring harnesses and associated connectors. The flexible circuits include substrates with conductive traces formed by a mechanical process such as dry milling a conductive layer on the substrates. PCB’s typically include connectors, terminals, and/or traces that are made of copper. Accordingly, the flexible circuits also typically use copper as the conductive material so that copper traces formed on the flexible circuits can be easily soldered or crimped to the copper connectors, terminals, and/or traces on the PCB’s.

[0041] Instead of copper, aluminum can be used as the conductive material on the flexible circuits since aluminum is lighter and cheaper than copper. However, aluminum traces on the flexible circuits cannot be easily soldered to copper connectors, terminals, and/or traces on the PCBs. This is because an oxide layer forms on the surface of the aluminum traces on the flexible circuits, which prevents solder from bonding with the aluminum traces.

[0042] The present disclosure provides various intermediate circuits (also called interposers) for connecting flexible circuits with aluminum traces to copper connectors, terminals, and/or traces on copper PCBs. The intermediate circuits are made of copper. The connectivity between the copper interposers and the aluminum traces on the flexible circuit is achieved by coating the aluminum traces on the flexible circuit with a pretreatment coating. The pretreatment coating cleans an oxide layer, which forms on the aluminum traces due to exposure to atmosphere during manufacture of the flexible circuit, off of the surface of the aluminum traces during the soldering process. The pretreatment coating on the aluminum traces can be cured at relatively low temperatures. The pretreatment coating sublimates due to the heat during the soldering process. The pretreatment coating on the aluminum traces is activated and removed from the aluminum traces due to heat during the soldering process, allowing the solder to wet the aluminum traces. The soldering process can include hot bar soldering or ultrasonic soldering.

[0043] The present disclosure is organized as follows. FIGS. 1-4 show an example of a flexible circuit made using a dry milling process and coated with a pretreatment layer. FIGS. 5-8 show examples of different interposer structures that can be used for soldering a flexible circuit including aluminum traces to copper terminals and traces on copper PCB’s. FIGS. 9A-9D show a flexible circuit including aluminum traces that are directly soldered to copper traces on copper PCB’s. FIGS. 10A and 10B show flexible heaters formed using flexible circuits including aluminum traces that can be connected to external circuitry by soldering copper wires to the aluminum traces. FIGS. 11 and 12 show dry milled conductive traces of the flexible circuits in further detail.

[0044] FIG. 1 shows a laminated substrate 50. The laminated substrate 50 includes a conductive layer 52 attached by an adhesive layer 54 to a support layer 58. In some examples, the support layer 58 is a flexible layer. In some examples, the support layer includes polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyimide (PI) layer, although other types of support layers can be used. In some examples, the conductive layer 52 includes copper, aluminum, an alloy, or another conductive material.

[0045] FIG. 2 shows conductive traces formed by a mechanical process such as dry milling. For example, the conductive layer 52 and the adhesive layer 54 of the laminated substrate 50 of FIG. 1 are dry milled to define one or more conductive traces 60-1 , 60-2 (collectively conductive traces 60). While only two conductive traces 60 are shown for simplicity of illustration, a plurality of conductive traces 60 can be formed. Specifically, portions of the conductive layer 52 and the adhesive layer 54 are removed (e.g., at 62) using the dry milling process to create the conductive traces 60.

[0046] A suitable example of a dry milling process is shown and described in commonly owned U.S. Patent No. 7,919,027 issued on April 5, 2011 and entitled “Methods and Devices for Manufacturing of Electrical Components and Laminated Structures”, which is hereby incorporated herein by reference in its entirety. [0047] During dry milling, a web of the laminated substrate 50 is fed between a milling wheel and a cliche. The cliche includes a pattern with raised and non-raised portions. The raised portions of the pattern push the laminated substrate 50 into the milling wheel in regions adjacent to the raised portions. The non-raised portions are not milled. The non-raised portions of the pattern define the conductive traces 60 in the conductive layer 52. The raised portions of the pattern define regions between the traces where the conductive layer 52 and the adhesive layer 54 are removed. The use of a mechanical process such as dry milling to create the conductive traces 60 eliminates the use of residual chemicals. The dry milled conductive traces 60 are shown and described below in further detail with reference to FIGS. 11 and 12.

[0048] FIG. 3 shows application of a pretreatment coating 64 to the conductive traces 60. After the mechanical structuring, layers of oxide and other contaminants may form on portions of the conductive traces 60. The pretreatment coating 64 is applied to the conductive traces 60 as shown in FIG. 3. The pretreatment coating 64 cleans the oxide layer off the surface of the conductive traces 60 during soldering. The pretreatment coating may also be optionally applied to a portion of the support layer 58.

[0049] For example, the pretreatment coating 64 can include compositions prepared as aqueous solutions or suspensions that can be applied to the aluminum surface to be soldered (e.g., the conductive traces 60 and other non-milled portions of the conductive layer 52) using printing techniques. The printable composition can be supplied as a gel or a cream. The composition can be cured, if necessary, by heating the structure shown in FIG. 3 at low temperatures that are compatible with plastic/polymer components of mass produced flex circuits.

[0050] FIG. 4 shows a solder material 70 dispensed or deposited on the pretreatment coating 64. The solder material 70 melts when heated. Before heating the solder material 70, a component such as an electronic component may be arranged on the solder material 70. For example, the electronic component may include a surface mount device (SMD), an application specific integrated circuit (ASIC), or any other component. Alternatively, other components such as terminals or headers of connectors, traces of PCB’s, and so on can be soldered to the conductive traces 60 as explained below in detail with reference to FIGS. 5-10B.

[0051] The pretreatment coating 64 is removed during the heating process, such as a soldering process performed in a reflow oven (or hot bar soldering or ultrasonic soldering), by localized heating of the pretreatment coating 64, to expose portions of the conductive traces 60. The exposed portions of the conductive traces 60 are connected by the melted solder material 70 to components such as terminals or traces of PCB’s to provide electrical connections therebetween.

[0052] Throughout the following description, various flexible circuits are shown, each of which can be manufactured using the methods described above with reference to FIGS. 1-3. Further, various structures for connecting a flexible circuit comprising aluminum conductive traces to copper components (e.g., copper terminals, copper wires, copper conductive traces on copper PCB’s, etc.) are shown for example only. In general, similar structures can be used to solder and connect a pair of any dissimilar metals. The structures can also be used to solder and connect aluminum to aluminum flexible circuits. Further, the genders of connectors/connections are mentioned for example only, and where suitable, an opposite gender than that described can be used instead.

[0053] FIG. 5 shows a side cross-sectional view of a flexible circuit 100 comprising aluminum traces connected to copper terminals 102 via an intermediate circuit (also called an interposer) 104 made of copper. The flexible circuit 100 comprises the conductive traces 60 formed on the support layer 58 as described above with reference to FIGS. 1-3. The adhesive layer 58 is omitted throughout the remaining figures for simplicity of illustration.

[0054] For example, the conductive traces 60 of the flexible circuit 100 are made of a first metal (e.g., aluminum). The conductive traces 60 of the flexible circuit 100 are coated with the pretreatment coating 64 before the flexible circuit 100 is soldered to the intermediate circuit 104 using the solder material 70 as described below. The pretreatment coating 64 is not shown since the pretreatment coating 64 is removed by the heat during the soldering process. The flexible circuit 100 further comprises a cover layer 110, which may be made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyimide (PI).

[0055] The intermediate circuit 104 comprises a support layer 120 and conductive traces 122 made from a conductive layer of a second metal (e.g., copper). The conductive layer of the second metal is attached to the support layer 120 by an adhesive layer similar to the adhesive layer 54 (not shown). The conductive traces 122 of the intermediate circuit 104 may be formed using a similar process used to form the conductive traces 60 of the flexible circuit 100 except that the pretreatment coating 64 is not applied to the conductive traces 122. The intermediate circuit 104 comprises a cover layer 124. For example, the support layer 120 and the cover layer 124 of the intermediate circuit 104 may be made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyimide (PI).

[0056] First ends of the conductive traces 122 made of copper are soldered to the conductive traces 60 made of aluminum. The soldering of the dissimilar metals (e.g., aluminum and copper) of the conductive traces 60, 122 is made possible by the application of the pretreatment coating 64 to the conductive traces 60 before soldering. The pretreatment coating 64 on the conductive traces 60 is activated and removed due to heat during the soldering process, allowing the solder material 70 to wet the aluminum conductive traces 60. The soldering process can include hot bar soldering or ultrasonic soldering. When the solder material 70 cools after the soldering process, a bond (connection) is formed between the conductive traces 122 made of copper and the conductive traces 60 made of aluminum. In some implementations, an electrically conducting connective glue may be used instead of the solder material 70 to bond the conductive traces 60, 122.

[0057] First ends of the copper terminals 102 include crimp fittings 105. The copper terminals 102 are crimped onto second ends of the conductive traces 122 by compressing or crimping the crimp fittings 105 around the second ends of the conductive traces 122. Thus, the first ends of the copper terminals 102 are connected to the conductive traces 60 made of aluminum via the conductive traces 122 (also made of copper) of the intermediate circuit 104.

[0058] For example, a distal end of the flexible circuit 100 may be connected to a first PCB (not shown), and the copper terminals 102 may be part of a connector 103 that is connected to a second PCB (not shown). For example, the copper terminals 102 may be of female type (i.e., second ends of the copper terminals 102 may be of the female type). The second ends of the copper terminals 102 can be inserted into the connector

103. The connector 103 can be mated with a male connector on the second PCB. Since the flexible circuit 100 is connected to the first PCB and the intermediate circuit

104, and since the intermediate circuit 104 with the copper terminals 102 soldered thereto can be directly plugged into a connector on the second PCB, a wiring harness that is typically used to connect the two PCB’s can be replaced by the flexible circuit 100 and the intermediate circuit 104.

[0059] FIG. 6 shows an arrangement similar to that shown in FIG. 5 except that pins 130, 132 of a dual-in-line connector 134 are soldered to the conductive traces 122 of the intermediate circuit 104. While not visible in the side cross-sectional view shown, the pins 130 and 132 are respectively connected to alternate ones of the conductive traces 122. The pins 130, 132 pass through the conductive traces 122 and are embedded in the support layer 120 of the intermediate circuit 104.

[0060] The pins 130, 132 are made of the same metal as the conductive traces 122 (e.g., copper) of the intermediate circuit 104. The conductive traces 122 are soldered (or glued) to the conductive traces 60 as described above with reference to FIG. 5. Accordingly, the pins 130, 132 made of copper are connected to the conductive traces 60 made of aluminum via the conductive traces 122 of the intermediate circuit 104.

[0061] The dual-in-line connector 134 including the pins 130, 132 can be connected to a suitable (female) connector on the second PCB to connect the second PCB via the intermediate circuit 104 and the flexible circuit 100 to the first PCB. If the connector on the second PCB is unsuitable (male), a wiring harness with suitable (female) connectors can be plugged into the dual-in-line connector 134 and into the connector on the second PCB to connect the second PCB via the intermediate circuit 104 and the flexible circuit 100 to the first PCB.

[0062] FIG. 7 shows an arrangement similar to that shown in FIG. 6 except that the pins 140, 142 of a dual-in-line connector 144 are right-angled while the pins 130, 132 of the dual-in-line connector 134 shown in FIG. 6 are vertical. All other connections and arrangements of other elements are the same as those described with reference to FIG. 6 and are therefore not described again for brevity.

[0063] FIG. 8 shows copper terminals 150 soldered directly to the aluminum conductive traces 60 of the flexible circuit 100. The copper terminals 150 are not crimped to the conductive traces 60. The copper terminals 150 differ from the copper terminals 102 shown in FIG. 5 in that the copper terminals 150 do not include the crimp fittings 105. Instead, the first ends of the copper terminals 150 are flat and can be soldered directly to the conductive traces 60 made of aluminum. The soldering of the dissimilar metals (e.g., aluminum and copper) of the terminals 150 and the conductive traces 60 is made possible by the application of the pretreatment coating 64 to the conductive traces 60 before soldering the terminals 150 to the conductive traces 60. This arrangement eliminates the intermediate circuit 104.

[0064] For example, the distal end of the flexible circuit 100 may be connected to a first PCB (not shown), and the copper terminals 150 may be part of a connector 152 that is connected to a second PCB (not shown). For example, the copper terminals 150 may be of female type (i.e., second ends of the copper terminals 150 may be of the female type). The second ends of the copper terminals 150 are inserted into the connector 152. The connector 152 can be mated with a male connector on the second PCB. Since the flexible circuit 100 is connected to the first PCB, and the connector 152 with the copper terminals 150 can be directly plugged into the connector on the second PCB, a wiring harness that is typically used to connect the two PCB’s is replaced by the flexible circuit 100 and the connector 152.

[0065] FIGS. 9A-9D show a method of connecting the aluminum conductive traces 60 of the flexible circuit 100 directly to copper conductive traces 162 of a PCB 160. FIG. 9A shows the flexible circuit 100 with the aluminum conductive traces 60 facing up. FIG. 9B shows the flexible circuit 100 with the aluminum conductive traces 60 facing down. FIG. 9C shows the PCB 160 with the copper conductive traces 162 (or pads of an edge connector of the PCB 160) facing up.

[0066] FIG. 9D shows the PCB 160 (as shown in FIG. 9C) with the aluminum conductive traces 60 of the flexible circuit 100 (as shown in FIG. 9B) soldered directly to the copper conductive traces 162 of the PCB 160. The soldering of the dissimilar metals (e.g., aluminum and copper) of the conductive traces 60, 162 is made possible by the application of the pretreatment coating 64 to the conductive traces 60 before soldering. This arrangement does not require any additional interconnecting components between the aluminum conductive traces 60 of the flexible circuit 100 and the copper conductive traces 162 of the PCB 160. Further, the copper conductive traces 162 of the PCB 160 may be made of copper, tin-plated copper, gold-plated copper, or electro-less nickel immersion gold (ENIG) plated copper.

[0067] Accordingly, using the pretreatment coating 64 or the electrically conductive glue with the hot bar soldering process allows splicing of flexible circuits made of dissimilar metals (e.g., aluminum and copper). These methods can also be used to splice aluminum to aluminum flexible circuits. The methods of splicing flexible circuits shown in FIGS. 5-9D can be used to eliminate wiring harnesses and connectors for a variety of applications. For example, in electric vehicles, the flexible circuits shown in FIGS. 5-9D can be used to eliminate wiring harnesses and connectors used between battery cells and PCB’s comprising circuits used to sense cell voltage and temperature and to charge the battery cells. Additional applications are contemplated.

[0068] FIG. 10A shows a flexible heater 200 formed using a flexible circuit 202. For example, the flexible circuit 202 may be formed using processes similar to those described with reference to FIGS. 1-3. For example, the flexible circuit 202 may include a conductive trace 204 made of a first metal (e.g., aluminum). For example, the conductive trace 204 may have a serpentine shape although any other shape may be used instead. The flexible heater 200 may further comprise first and second cover layers (not shown), each made of PET, PEN, or PI, arranged respectively on top of the conductive trace 204 and on the bottom of the flexible circuit 202.

[0069] The flexible circuit 202 may optionally comprise a pair of pads 210, 212 that are also made of the first metal (e.g., aluminum). The pair of pads 210, 212 can be used to connect the flexible circuit 202 to an external circuit such as a power supply (not shown). For Example, two wires 214, 216 made of a second metal (e.g., copper) may be respectively soldered to the pads 210, 212 (if used). Alternatively, the pads 210, 212 are not provided, and the two wires 214, 216 may be directly soldered to first and second ends of the conductive trace 204, respectively.

[0070] For example, the wires 214, 216 may include multi-strand wires. The soldering of the dissimilar metals (e.g., aluminum and copper) of the wires 214, 216 and the conductive trace 204 (or the pads 210, 212 if used) is made possible by the application of the pretreatment coating 64 to the conductive trace 204 (or pads 210, 212 if used) before soldering. For example, the distal ends of the wires 214, 216 may be connected to a connector 218. The connector 218 can be connected to an external circuit such as a power supply (not shown) that can supply power to the flexible circuit 202 that can be used as a heater.

[0071] FIG. 10B shows another flexible heater 250 formed using a flexible circuit 252. For example, the flexible circuit 252 may be formed using processes similar to those described with reference to FIGS. 1-3. For example, the flexible circuit 252 may include a plurality of conductive traces 254-1 , 254-2, ... , and 254-N (collectively the conductive traces 254), where N is an integer greater than 1 . The conductive traces 254 are made of a first metal (e.g., aluminum). For example, the conductive traces 254 may have a shape of a loop although any other shape may be used instead. The conductive traces 254 are not connected to each other. That is, each conductive trace 254 is a separate and independent circuit. The flexible heater 250 may further comprise first and second cover layers (not shown), each made of PET, PEN, or PI, arranged respectively on top of the conductive traces 254 and on the bottom of the flexible circuit 252.

[0072] The flexible circuit 252 may further optionally comprise pairs of pads (260-1 , 262-1 ), (260-2, 262-2), ... , and (260-N, 262-N), which are collectively called the pairs of pads 260, 262, where N is an integer greater than 1 . The pairs of pads 260, 262 are also made of the first metal (e.g., aluminum). Each pair of pads 260, 262 may be connected to first and second ends of a separate one of the conductive traces 254, respectively.

[0073] Pairs of wires (264-1 , 266-1 ), (264-2, 266-2), ... , and (264-N, 266-N), which are collectively called pairs of wires 264, 266, where N is an integer greater than 1 , may be soldered to the pairs of pads 260, 262 (if used). Alternatively, the pairs of pads 260, 262 may be omitted, and the pairs of wires 264,266 may be directly soldered to first and second ends of the conductive traces 254, respectively. Accordingly, power supply to each conductive trace 254, which forms a separate heater, can be individually or independently controlled.

[0074] The pairs of wires 264, 266 are made of a second metal (e.g., copper) and may include multi-strand wires. The soldering of the dissimilar metals (e.g., aluminum and copper) of the pairs of wires 264, 266 and the conductive traces 254 (or the pairs of pads 206, 262 if used) is made possible by the application of the pretreatment coating 64 to the conductive traces 254 (or the pairs of pads 206, 262 if used) before soldering. For example, the distal ends of the pairs of wires 264, 266 may be connected to a connector 268. The connector 268 can be connected to an external circuit such as a power supply (not shown) that can supply power to the flexible circuit 252.

[0075] The flexible heaters 200, 250 of FIGS. 10A and 10B can be used in a variety of applications. For example, the flexible heaters 200, 250 can be used to heat batteries in vehicles. Additionally, the flexible heaters 200, 250 can be used as electric blankets. Many other applications are contemplated.

[0076] FIGS. 11 and 12 show side cross-sectional views of a conductive trace formed by a mechanical process such as dry milling. FIG. 11 shows a conductive trace formed by removing portions of the conductive layer 52 and the adhesive layer 54 (see FIG. 1 ) by using a mechanical process such as dry milling. FIG. 12 shows a conductive trace formed by removing portions of the conductive layer 52 (the adhesive layer 54 is not used) by using a mechanical process such as dry milling.

[0077] In FIG. 11 , the dry milling process produces the conductive traces 60 having a pyramid-like shape or a trapezoidal shape. Specifically, using the dry milling process, the conductive layer 52 (see FIG. 1 ) is cut such that the edges of the conductive traces 60 taper downwards and outwardly towards the adhesive layer 54 and the support layer 58 at an acute angle relative to an axis perpendicular to the plane of the layers 52, 54, 58. The edges of the conductive traces 60 taper outwardly relative to the center of the conductive traces 60.

[0078] Further, the adhesive layer 54 is also cut along the same acute angle. As a result, the edges of the adhesive layer 54 also taper downwards and outwardly towards the support layer 58 at the acute angle relative to an axis perpendicular to the plane of the support layer 58. The edges of the adhesive layer 54 taper outwardly relative to the center of the conductive traces 60. The edges of the adhesive layer 54 extend outwardly beyond the edges of the conductive traces 60. The edges of the adhesive layer 54 are aligned with the edges of the conductive traces 60.

[0079] Accordingly, while the undercuts 88 produced by the chemical etching process weaken or erode the support under the edges of the conductive traces 60, the dry milling process reinforces or strengthens support under the edges of the conductive traces 60. This enhances the quality bonding of components to the conductive traces 60-1 , 60-22 (e.g., by soldering, welding, etc.) and increases the life of the flex circuits formed using the dry milling process.

[0080] In FIG. 12, the adhesive layer 54 is not used. Similar to FIG. 11 , the dry milling process produces the conductive traces 60 having a pyramid-like shape or a trapezoidal shape. Specifically, using the dry milling process, the conductive layer 52 (see FIG. 1 ) is cut such that the edges of the conductive traces 60 taper downwards and outwardly towards the support layer 58 at an acute angle relative to an axis perpendicular to the plane of the support layer 58. The edges of the conductive traces 60 taper outwardly relative to the center of the conductive traces 60. The dry milling process extends and removes a relatively small portion of the support layer 58 as shown at 97. The extent or the depth of the portion 97 is controlled during dry milling and is not detrimental to the quality and life of the flex circuit. [0081] While the methods of the present disclosure can be used to connect PCB’s and other assemblies in general, the methods can be particularly useful to connect sensing circuits to batteries in electric vehicles. Other applications of the methods include connecting preamplifiers to rotating storage assemblies (e.g., in disk drives), connecting print-heads to control circuits in printers, connecting sensors and transducers in control circuits in medical equipment and semiconductor manufacturing equipment, and so on.

[0082] The foregoing description is merely illustrative in nature and is not intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.

[0083] Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.

[0084] Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

Claims

CLAIMS What is claimed is:

1 . A flexible circuit comprising: a laminated substrate comprising: a support layer; and a conductive layer made of a first metallic material arranged on the support layer, wherein the conductive layer includes conductive traces of the first metallic material; and a layer of a pretreatment coating deposited on the conductive traces; and a component made of a second metallic material soldered to the conductive traces, wherein the soldering sublimates the pretreatment coating.

2. The flexible circuit of claim 1 wherein the first metallic material includes aluminum and the second metallic material includes copper.

3. The flexible circuit of claim 1 wherein the first and second metallic materials include aluminum.

4. The flexible circuit of claim 1 wherein the component comprises: a second laminated substrate comprising: a second support layer; and a second conductive layer made of the second metallic material arranged on the second support layer, wherein the second conductive layer includes second conductive traces of the second metallic material that are respectively soldered to the conductive traces of the laminated substrate.

5. The flexible circuit of claim 4 further comprising a plurality of terminals of a connector that are made of the second metallic material and that are soldered respectively to the second conductive traces on opposite ends relative to the conductive traces.

6. The flexible circuit of claim 5 further comprising the connector wherein the plurality of terminals is inserted into the connector.

7. The flexible circuit of claim 4 further comprising a dual in line connector including pins made of the second metallic material soldered respectively to the second conductive traces on opposite ends relative to the conductive traces.

8. The flexible circuit of claim 7 wherein the pins are vertical.

9. The flexible circuit of claim 7 wherein the pins are right-angled.

10. The flexible circuit of claim 1 wherein the component comprises a plurality of terminals of a connector respectively soldered to the conductive traces.

11. The flexible circuit of claim 10 further comprising the connector wherein the plurality of terminals is inserted into the connector.

12. The flexible circuit of claim 1 wherein the component includes a printed circuit board (PCB) comprising: a second support layer; and a second conductive layer made of the second metallic material arranged on the second support layer, wherein the second conductive layer includes second conductive traces of the second metallic material that are respectively soldered to the conductive traces of the laminated substrate.

13. The flexible circuit of claim 1 wherein the conductive traces are connected in series to form a loop having a first end a second end and wherein the component comprises: a first wire soldered to the first end of the loop; and a second wire soldered to the second end of the loop.

14. The flexible circuit of claim 13 further comprising a connector wherein distal ends of the first and second wires are connected to the connector.

15. The flexible circuit of claim 1 wherein the conductive traces are connected to form N separate loops, where N is an integer greater than 1 , each of the N loops having a first end a second end; wherein the component comprises N pairs of wires; and wherein: a first wire in the Nth pair of wires is soldered to the first end of the Nth loop; and a second wire in the Nth pair of wires is soldered to the second end of the Nth loop.

16. The flexible circuit of claim 15 further comprising a connector wherein distal ends of the N pairs of wires are connected to the connector.

17. The flexible circuit of claim 1 wherein: the laminated substrate is dry milled to form the conductive traces; and edges of the conductive traces taper outwardly and towards the support layer.

18. The flexible circuit of claim 1 further comprising an adhesive layer disposed between the conductive layer and the support layer, wherein: the laminated substrate is dry milled to form the conductive traces; edges of the conductive traces and the adhesive layer taper outwardly and towards the support layer; and the edges of the adhesive layer are aligned with the edges of the conductive traces.

19. The flexible circuit of claim 1 wherein the support layer includes a material selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI).

20. The flexible circuit of claim 1 further comprising a cover layer covering the conductive traces wherein the cover layer includes a material selected from a group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI).

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