Installing a pin holder using a laser welding process

Abstract

The present disclosure relates to installing a pin holder using a laser welding process. A substrate includes a copper trace. A copper pin holder has a hollow cylindrical member with a flange member. The flange member of the copper pin holder is held in contact with the copper trace. A laser beam is then applied to an upper surface of the flange member to form at least one direct copper-to-copper tack weld between the flange member of the pin holder and the copper trace. The hold on the copper pin holder is then released. The laser beam is then again applied to the upper surface of the flange member at a starting location and the applied laser beam is moved along a circumferential trace path around a perimeter of the hollow cylindrical member of the pin holder to form direct copper-to-copper welds between the flange member of the pin holder and the copper trace.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 782,290, filed April 2, 2025, the contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to a process for mounting lead holders to a substrate using a direct copper-to-copper bond formed by laser welding. Background Technology

[0004] Many circuit device applications require lead holders that must be mounted to a bottom substrate. Such substrates can include ceramic substrates using active metal brazing (AMB) technology, which are well-suited for use in electronic devices requiring high voltage / current conductivity and good thermal / mechanical stability. A copper-based material layer is applied to the surface of the ceramic substrate, which is then heated to a high temperature in the presence of a reducing gas atmosphere. This causes the copper-based material to react with the ceramic and form a strong chemical bond, allowing the metal layer to bond to the ceramic substrate. The copper layer can then be coated with a silver layer.

[0005] In conventional processes, to mount lead holders onto a ceramic substrate, the lead holder is positioned at a desired location on the substrate, for example using pick-and-place machines, and attached to the substrate using a solder sintering process. This conventional process for lead holder mounting has several drawbacks, including but not limited to: the need for a silver layer in the solder paste sintering process, which increases additional cost and processing time; the requirement to cure the formed joint in a reflow oven; the need for flux cleaning after solder curing; and the need for automated optical inspection to ensure the accuracy of the joint. Furthermore, the joint strength is highly dependent on and limited by the materials used, the applied mechanical stress, and the applied heat.

[0006] There is a need in the field for a simpler pin retainer mounting process that offers space and cost savings, as well as process and quality improvements, compared to conventional solder sintering processes. Summary of the Invention

[0007] In one embodiment, a method includes: holding a copper lead holder in contact with a copper trace on a substrate, the copper lead holder having a hollow cylindrical member with a flange member in contact with the copper trace; applying a laser beam to an upper surface of the flange member to form at least one direct copper-to-copper positioning weld between the flange member of the lead holder and the copper trace; releasing the holding of the copper lead holder attached to the copper trace by the at least one direct copper-to-copper positioning weld; and applying the laser beam to the upper surface of the flange member at a starting position and moving the applied laser beam along a circumferential trace path around the periphery of the hollow cylindrical member of the lead holder to form a direct copper-to-copper weld between the flange member of the lead holder and the copper trace.

[0008] In one embodiment, an apparatus includes: a substrate having copper traces; a copper pin holder on the copper traces, the copper pin holder having a hollow cylindrical member with a flange member in contact with the copper traces; and a direct copper-to-copper solder joint between the flange member of the pin holder and the copper traces, the direct copper-to-copper solder joint following a circumferential trace path around the periphery of the hollow cylindrical member of the pin holder.

[0009] The direct copper-to-copper welding includes at least one direct copper-to-copper positioning weld between the flange member of the pin holder and the copper trace. Attached Figure Description

[0010] To better understand the embodiments, reference will now be made to the accompanying drawings by way of example only, wherein:

[0011] Figure 1 This is a perspective view of the pin holder mounted on the bottom substrate;

[0012] Figure 2 It is a cross-sectional scanning electron micrograph (SEM) image of a lead holder mounted to a substrate by laser welding to form a direct copper-to-copper bond.

[0013] Figure 3A-3L The steps in the process of laser bonding lead holders to a substrate are shown; and

[0014] Figure 4 It shows that it includes those that have been used. Figure 3A-3L A perspective photograph of a circuit device that is laser-welded to a substrate by means of multiple pin holders. Detailed Implementation

[0015] Now for reference Figure 1The diagram shows a perspective view of a lead holder 10 mounted to a bottom substrate 20. The lead holder 10 includes a hollow cylindrical member 12 having a first end 14 and a second end 16, and a flange member 18 at the second end 16. The lead holder 10 is made of a copper-based material. The substrate 20 is, for example, an active metal brazing (AMB) ceramic substrate, including a ceramic substrate portion 22 and a copper-based material trace 24. Notably, and advantageously from a cost and processing time perspective, there is no silver layer on the upper surface of the copper-based material trace 24. The attachment of the lead holder 10 to the substrate 20 is achieved by using a direct copper-to-copper bond formed using a laser welding process. The bonding locations are typically schematically shown in... Figure 1 The figure shows the location of the laser path trace forming the weld, indicated by reference numeral 30 (also called weld 124). A joint is formed between the flange member 18 of the pin holder 10 and the copper-based material trace 24 circumferentially surrounding the second end 16 of the hollow cylindrical member 12.

[0016] For reference purposes, the example dimensions of the lead holder 10 include: overall height 2.8 mm; flange member diameter 2.2 mm; flange member thickness 0.4 mm; cylindrical member outer diameter 1.0 mm; and cylindrical member inner diameter 0.70 mm. However, it will be understood that lead holders 10 with different dimensions may be used depending on the circuit or device application.

[0017] Although embodiments for bonding with AMB technology ceramic substrates are shown, it will be understood that bonding of lead holders with other copper-based material substrates is within the scope of this invention.

[0018] Figure 2 A cross-sectional image of a lead holder 10 for a copper-based material trace 24 mounted to a substrate 20 via a direct copper-to-copper bond formed by laser welding is shown. The laser-welded joint at the flange member 18 is generally indicated by reference numeral 30 within the elliptical area used for welding 124.

[0019] Now for reference Figure 3A-3L It illustrates the steps in the process of laser welding the pin holder 10 to the substrate 20.

[0020] Figure 3A - The pick-and-place machine 100 places the lead holder 10 at a desired location on the substrate 20. Specifically, the hollow cylindrical member 12 of the lead holder 10 is engaged by the clamping member 102 of the pick-and-place machine 100, and the flange member 18 of the lead holder 10 is placed and held to contact the upper surface of the copper-based material trace 24 of the substrate 20 at the desired mounting location.

[0021] Figure 3B -shown Figure 3A Top view.

[0022] Figure 3C -With the pick-and-place machine 100 holding the pin holder 10 at a desired position on the substrate 20, the laser welding machine 110 applies a laser beam 112 at two or more selected discrete locations on the upper surface of the flange member 18 to provide a direct copper-to-copper positioning weld (i.e., pre-weld) 114 between the flange member 18 and the copper-based material trace 24. For example, the weld depth can be approximately 50% of the total thickness of the copper-based material trace 24 (as a non-limiting example, for a flange 18 thickness of 0.4 mm and a copper-based material trace 24 thickness of 0.8 mm, the weld depth would be approximately 0.4 mm deep, extending completely through the flange and reaching a depth of approximately 0.4 mm in the copper-based material trace; see also...). Figure 2 (Cross-section). The laser welding machine 110 may, for example, include a fiber laser from IPG Photonics, which includes a robot positioning and movement system. The fiber laser may have a power of approximately 4 kW, a beam size of 50 μm, and a red beam pulsed at 1064 Hz to perform direct copper-to-copper welding. The operation of the laser can be optimized to achieve rapid weld penetration when forming the positioning weld 114. The position, depth, width, and length of the laser welding and penetration can be controlled through operating parameter settings, equipment configuration, and programmed movement.

[0023] Figure 3D - This shows two positioning welds 114 in place. Figure 3C Top view. The locating welds 114 can be spaced equally apart from each other in the circumferential direction as desired (the 180° spacing shown for two such welds is only an example - and it is understood that in some cases three, four or more locating welds may be used).

[0024] Figure 3E Then the gripping member 102 of the pick-and-place machine 100 releases its holding on the pin holder 10. As the gripping pressure of the gripping member 102 of the pick-and-place machine 100 is released, Figure 3C The use of pre-soldering cycles to provide two or more positioning solders 114 effectively secures the lead holder 10 in the desired position on the substrate 20. This pre-soldering cycle ensures that the desired positioning of the lead holder 10 is not disturbed by the subsequent full soldering cycle.

[0025] Figure 3F -shown Figure 3E Top view.

[0026] Figure 3GThen, during a full welding cycle, the laser welding machine 110 applies a laser beam 112 to the upper surface of the flange member 18, starting from a position 120 that is circumferentially offset from the position of the previously manufactured positioning weld 114.

[0027] Figure 3H -shown Figure 3G A top view. Here, by way of example only, the starting position 120 is shown to be circumferentially spaced apart from two circumferentially adjacent positioning welds 114.

[0028] Figure 3I Then, the laser welding machine 110 moves the applied laser beam 112 clockwise or counterclockwise along the circumferential trace path (indicated by arrow 122) around the periphery of the hollow cylindrical member 12 of the lead holder 10 to form a direct copper-to-copper weld 124 from the lead holder 10 to the copper-based material trace 24. For example, the weld depth can be approximately 50% of the total thickness of the copper-based material trace 24 (as a non-limiting example, for a flange 18 thickness of 0.4 mm and a copper-based material trace 24 thickness of 0.8 mm, the weld depth completely penetrates the flange and reaches a depth of approximately 0.4 mm in the copper-based material trace; see [link to documentation]). Figure 2 (Cross-section). Here, again, the laser welding machine 110 may include, for example, a fiber laser from IPG Photonics, which includes a robot positioning and movement system. The fiber laser may have a power of approximately 4 kW, a beam size of 50 μm, and a red beam pulsed at 1064 Hz to enable direct copper-to-copper welding. The operation of the laser can be optimized to achieve rapid weld penetration and scanning along any desired trace path 122 to form a weld 124. The position, depth, width, and length of the laser welding and penetration can be controlled by setting operating parameters, configuring the equipment, and programming movement. In a preferred embodiment, the formed weld is continuous along the circumferential trace path 122 and completely surrounds the periphery of the hollow cylindrical member 12 of the pin holder 10 (but it should be noted that discontinuous weld segments along the circumferential trace path 122 around the periphery of the hollow cylindrical member 12 can also be used alternatively).

[0029] Figure 3J and Figure 3K -shown Figure 3I Top view. Figure 3J The illustration shows a laser weld of approximately 230° along a complete 360° circumferential trace path 122. Figure 3K This demonstrates the complete completion of laser welding in a full welding cycle, forming weld 124 at least along a 360° circumferential trace path.

[0030] Figure 3L- A photograph of the pin holder 10 is shown, in which the flange member 18 is mounted to the copper-based material trace 24 of the substrate 20 via direct copper-to-copper circumferential bonding 124.

[0031] Alternatively, the laser beam 112 applied by the laser welding machine 110 during a full welding cycle can move more than 360° along the circumferential trace path 122. For example, the completion of the laser welding process in a full welding cycle may include applying a circumferentially moving laser beam 112 to include an additional 20° to 40° overlap (i.e., tracing the path 122 at 380° to 400°). Further additional overlap would still be useful: for example, in the range of 500° to 600° (one and a half turns); or in the range of 720° to 800° (two or more turns).

[0032] Compared to previous mounting solutions, laser welding for mounting pin holders offers numerous advantages, including: stronger interconnects; deeper interconnect penetration; independent control over pattern, area, and depth; better speed: improved cycle time / faster welding time; greater cost-effectiveness: replacing multiple processes and simplifying process steps; higher precision enabling more precise control over pin holder accuracy; improved process consistency and reliability; greater versatility: reduced material (plating), machine, and tooling costs; greater flexibility in welding dissimilar metals; no need for any solvents or additives, and no need for chemical cleaning; better reliability: improved fatigue due to the coefficient of thermal expansion (CTE) at the joint and increased reliability under higher current / voltage limits; and support for welding thicker materials (depending on the laser system).

[0033] Advantageously, especially compared to the previous sintering process using solder paste, the use of laser welding for direct copper-to-copper bonding eliminates the need for additional bonding materials (such as silver plating or paste application at the joint); it welds two raw materials (copper and copper in the example) together to form a strong intermetallic weld capable of withstanding high stress and heat; and it eliminates the need for curing or cleaning processes.

[0034] By using laser soldering for direct copper-to-copper bonding, the mounting process: reduces the required process steps; eliminates the need for screen printing (thus eliminating stencil design and costs, and adapting to changes in different products); eliminates the need for plating to support adhesion; eliminates the need for flux cleaning and reflow; eliminates the need for automated optical inspection for process control; minimizes machine / maintenance / tooling costs and floor space; eliminates concerns about potential voids, pin retainer misalignment, or flange delamination due to reflow; provides improved joint strength and less temperature sensitivity; eliminates concerns about fatigue caused by CTE mismatch or adversely affecting product reliability; and supports direct material interconnection for strong joints.

[0035] Although the invention has been illustrated and described in detail in the accompanying drawings and foregoing description, such illustrations and descriptions are intended to be illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments will be understood and implemented by those skilled in the art in practicing the claimed invention, through study of the drawings, disclosure, and appended claims.

Claims

1. A method comprising: A copper lead holder is held in contact with a copper trace on a substrate. The copper lead holder has a hollow cylindrical member with a flange member that contacts the copper trace. A laser beam is applied to the upper surface of the flange member to form at least one direct copper-to-copper positioning solder joint between the flange member and the copper trace of the pin holder. Release the holding of the copper pin holder attached to the copper trace via the at least one direct copper-to-copper positioning solder; and The laser beam is applied to the upper surface of the flange member at the starting position, and the applied laser beam is moved along a circumferential trace path around the periphery of the hollow cylindrical member of the pin holder to form a direct copper-to-copper solder joint between the flange member of the pin holder and the copper trace.

2. The method according to claim 1, wherein the starting position is circumferentially offset relative to the position of the at least one direct copper-to-copper positioning weld.

3. The method of claim 1, wherein the direct copper-to-copper solder follows the circumferential trace path at least 360°.

4. The method of claim 1, wherein the direct copper-to-copper solder follows the circumferential trace path at at least 400°.

5. The method of claim 1, wherein the direct copper-to-copper solder follows the circumferential trace path at at least 500°.

6. The method of claim 1, wherein the direct copper-to-copper solder follows the circumferential trace path at least 720°.

7. The method of claim 1, wherein the direct copper-to-copper welding is continuous along the circumferential trace path.

8. The method of claim 1, wherein applying the laser beam to form at least one direct copper-to-copper locating weld comprises forming at least two circumferentially spaced direct copper-to-copper locating welds.

9. The method of claim 8, wherein the at least two circumferentially spaced direct copper-to-copper positioning welds are equally spaced in the circumferential direction.

10. The method of claim 9, wherein the starting position is equally spaced circumferentially between adjacent direct copper-to-copper locating welds in the at least two circumferentially spaced direct copper-to-copper locating welds.

11. An apparatus comprising: Substrate with copper traces; A copper lead holder on the copper trace, the copper lead holder having a hollow cylindrical member with a flange member, wherein the flange member contacts the copper trace; and A direct copper-to-copper solder joint is formed between the flange member of the pin holder and the copper trace, the direct copper-to-copper solder joint following the circumferential trace path around the periphery of the hollow cylindrical member of the pin holder.

12. The apparatus of claim 11, wherein the direct copper-to-copper solder follows the circumferential trace path at least 360°.

13. The apparatus of claim 11, wherein the direct copper-to-copper solder follows the circumferential trace path at at least 400°.

14. The apparatus of claim 11, wherein the direct copper-to-copper solder follows the circumferential trace path at at least 500°.

15. The apparatus of claim 11, wherein the direct copper-to-copper solder follows the circumferential trace path at at least 720°.

16. The apparatus of claim 11, wherein the direct copper-to-copper welding is continuous along the circumferential trace path.

17. The apparatus of claim 11, wherein the direct copper-to-copper soldering comprises at least one direct copper-to-copper positioning soldering between the flange member of the pin holder and the copper trace.

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