Extended pad region to prevent damage to printed circuit board

Abstract

A printed circuit board having an electrically insulating layer and a conductive solder pad. The conductive solder pad is at least partially disposed over the electrically insulating layer and defines a solder contact area. The solder contact area is configured for establishing an electrical connection with an electrical component via laser welding. The printed circuit board further includes a solder mask that coats the conductive solder pad and defines an exposed region of the conductive solder pad. The conductive solder pad protects the electrically insulating layer from incident heat during the laser soldering by extending a length below the solder mask along a periphery of the exposed region.

Description

Technical Field

[0001] The presently disclosed subject matter relates to printed circuit boards, and more particularly to preventing damage to solder pads of a printed circuit board during laser soldering. Background Art

[0002] A printed circuit board is a multilayer structured device that makes electrical connections between electronic components. The layers of a printed circuit board may vary, but are generally composed of a base material and a copper foil laminate that are pressed together and cured with heat to form the core of the printed circuit board. Multiple layers of conductive material are arranged alternately with electrically insulating layers. The metal layers of a printed circuit board can be etched to form electrical traces that construct the circuit. Multiple conductive layers can also be connected to each other through vias. The top metal layer in a printed circuit board is coated with a solder mask layer. The solder mask layer defines the perimeter of the solder pads, i.e., the metal areas that are exposed and can be used to make electrical connections.

[0003] Laser welding is a process used to establish electrical connections with solder pads on printed circuit boards. Solder pads are typically designed with specific sizes and shapes to match the corresponding leads of the components they are intended to accommodate. The size and shape of the solder pads can affect the soldering process, heat distribution, and the overall mechanical and electrical performance of the connection. A known problem with laser welding is the potential for laser damage to materials adjacent to the solder pads due to laser misalignment. This scorching occurs because the printed circuit board composite material cannot withstand the intense localized heating when directly hit by the laser. The laser light can also be reflected from the solder material onto the printed circuit board and is another potential source of heat that can cause damage and require mitigation. Excessive heat can cause delamination of the printed circuit board or damage the necessary insulating properties of the composite material. If the insulation between the two metal layers is damaged, the circuit is destroyed and the device fails.

[0004] Protecting printed circuit boards from damage caused by laser welding is a known challenge within the electronics industry. There are some disclosures for addressing this problem. In one such disclosure (U.S. Patent No. 10,772,214B2), pins are inserted into through holes of solder contacts and soldered in place. The white coating on the solder contacts reflects the laser beam, and the angle of the laser beam is adjusted to reduce the energy absorption rate and inhibit damage to insulating parts. The irradiation angle of the laser beam used for welding is adjusted relative to the circuit board so that the laser light reflected from the terminal pins irradiates the white layer on the solder contacts. Reflection from the white coating on the board and adjusting the laser angle prevents overheating of the insulating components.

[0005] In U.S. Pat. No. 7,134,592 B2, a temperature-sensitive electronic component connected to a board by soldering during the mounting process is protected from heat during the soldering process in order to prevent permanent damage to the component. The solder connection of the component is thermally coupled to the protective device during the soldering process so that some of the heat introduced into the solder connection during the soldering process is transferred to the protective device. The protective device also has a protective sleeve that surrounds the component in an appropriate position. The protective sleeve is made of a heat-insulating material, and a coating with high heat reflectivity is provided at an appropriate position on the outer wall of the protective sleeve facing away from the component.

[0006] In Japanese Patent No. 2014107424A, the shape of the lead portion of the terminal of the electronic component is configured to prevent the surface of the circuit board from being burned by melting the solder by the laser beam. In an electronic circuit device including a circuit board on which the electronic component is mounted, the terminal of the electronic component inserted into the through hole is bonded to the solder contact on the circuit board via the solder melted by the laser beam emitted from the laser light source. The shape of the lead end portion of the terminal of the electronic component and the exposed edge of the terminal are set so that the direct light from the laser light source and the light reflected by the lead end portion of the terminal do not overlap on the surface of the circuit board other than the solder contact.

[0007] In Japanese Patent No. 2006173282A, a method for providing electronic parts welding and a device with a simple structure, by which a substrate can be protected from burning, is designed. The welding method is a method for welding the leads of electronic parts to the solder contacts of a printed board by irradiating with a laser beam. In this method, a light shielding member equipped with a cylinder (the inner circumference of the cylinder is almost equal to the outer circumference of the solder contact in the plane direction of the solder contact forming surface of the printed board) is arranged on the surface of the substrate in the following manner: one open end of the light shielding member is placed against the surface so that the insertion tip of the lead and the pad are included in its opening area to prevent the surface of the substrate of the printed board around the pad from being directly and / or indirectly irradiated by the laser beam (reflected beam), and the lead is irradiated with the laser beam through the cylinder. Summary of the invention

[0008] Laser welding is a precision welding technology that uses a laser beam to heat and melt solder material to join two or more components together, such as joining a conductive wire to a contact pad. In it, a focused laser beam is directed onto the solder joint, providing localized and controlled heating. The energy from the laser beam is absorbed by the solder material, which causes the solder material to melt. After cooling, a strong bond is formed between the welded parts. Solder pads are necessary to provide a means of protecting the composite layer structure of a printed circuit board from damage. An improved design of a solder pad on a printed circuit board is discussed in this article, and achieves the goal of protecting the composite layer structure more effectively and efficiently than existing solutions in the industry.

[0009] Embodiments of the present disclosure include a printed circuit board. The printed circuit board has an electrically insulating layer and a conductive solder pad at least partially disposed above the electrically insulating layer. The conductive solder pad defines a solder contact area configured to establish an electrical connection with an electrical component via laser welding. The printed circuit board further includes a solder mask that coats the conductive solder pad and defines an exposed area of ​​the conductive solder pad. The conductive solder pad protects the electrically insulating layer from incident heat during the laser welding by extending a length below the solder mask along the periphery of the exposed area.

[0010] In another embodiment, the extended length of the conductive solder pad can depend on the height and width of the solder contact area or on the minimum reflection angle, which takes into account the laser reflection outside the solder contact area during laser welding. However, the extended length of the conductive solder pad can further depend on the maximum reflection angle, which includes the minimum reflection angle and the supplementary reflection angle, which takes into account the changes during part tolerances, conductor placement and / or laser welding. The range of reflection angles that take into account the changes during part tolerances, conductor placement and / or laser welding can be between 5 and 30 degrees. This range provides a balance between the minimum amount of protection and the maximum amount of protection before the solder pad becomes a large enough heat sink to degrade the quality of the resulting solder joint. In another embodiment, the range is 10 to 25 degrees.

[0011] The extended length of the conductive solder pad can be determined by the following equation:

[0012]

[0013] in:

[0014] W ep is the extended length of the conductive solder pad;

[0015] H c and W c are the height and width of the solder contact area of ​​the conductive solder pad, respectively;

[0016] θ sa is the minimum reflection angle that takes into account the laser reflection outside the solder contact area during laser welding;

[0017] φ is the supplemental reflection angle that accounts for part tolerances, conductor placement, and / or variations during laser welding; and

[0018] W sa is the width of the conductive solder pad.

[0019] In an embodiment of the present disclosure, the conductive solder pad can be arranged completely around the periphery of the solder contact area, except for the channel in the printed circuit board for receiving the conductive wire, thereby providing thermal protection in all directions relative to the solder contact area. The extension length of the conductive solder pad can be 0.25 to 2.5 mm.

[0020] Embodiments of the present disclosure include a printed circuit board. The printed circuit board has an insulating layer and a copper pad disposed above the insulating layer, the copper pad defining a solder contact area for soldering a component thereto. The printed circuit board also has a solder mask layer disposed above the copper pad. The copper pad extends below the solder mask layer to protect the insulating layer during soldering.

[0021] In yet another embodiment, the copper pad extends beneath the solder mask layer along a periphery of the solder contact area, or extends beneath the solder mask layer along a periphery of the solder contact area, except for channels in the printed circuit board for receiving conductive traces.

[0022] Embodiments of the present disclosure include a method for manufacturing a printed circuit board. The method includes positioning an electrically insulating base layer and a solder pad adjacent to the electrically insulating base layer, the solder pad defining an electrical contact area. The method further includes the step of coating the solder pad with a solder mask so that the solder pad extends a distance below the solder mask and the electrical contact area remains exposed. Finally, the method includes the step of laser welding a conductive line to the electrical contact area, the solder pad protecting the electrically insulating base layer from damage caused during laser welding by extending below the solder mask. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Various aspects of the present disclosure are discussed herein with reference to the accompanying drawings. It should be understood that, for simplicity and clarity of illustration, the elements shown in the drawings are not necessarily drawn accurately or to scale. For example, for clarity, the size of some elements may be enlarged relative to other elements, or several physical components may be included in a functional block or element. In addition, where deemed appropriate, reference numerals may be repeated in the drawings to indicate corresponding or similar elements. However, for clarity, not every component may be labeled in every drawing. The drawings are provided for the purpose of illustration and explanation and are not intended to be a definition of limitations of the present disclosure.

[0024] Figure 1 A schematic diagram showing a cross section of a conventional printed circuit board showing variable layers.

[0025] FIG. 2A to FIG. 2B A top perspective view of an example sample of damage caused to a printed circuit board during laser welding is shown. Excessive heat can cause delamination of the printed circuit board or damage the necessary insulating properties of the composite material. If the insulation between two metal layers is damaged, the circuit is destroyed and device failure may occur.

[0026] Figure 3 A top plan view of a solder mask defining solder contact areas for soldering wires is shown.

[0027] FIG. 4A to FIG. 4B Two top plan views of the solder pad are shown. Figure 4A The designs and Figure 4B The solder pad design of the present disclosure is compared. Figure 4B In PCB, the area of ​​the solder pad extends beyond the area exposed by the solder mask to protect the underlying and adjacent substrate material. If heat is applied outside the solder area, the extended pad absorbs the heat and the printed circuit board is not damaged.

[0028] FIG. 5A to FIG. 5B A top plan view of a 2.5 mm wide solder contact is shown. By increasing the size of the solder pad under the solder mask to have a 0.50 mm wide protective border area, as shown in FIG. Figure 5B As shown, the underlying and adjacent insulating substrate material is protected from thermal damage caused by laser welding.

[0029] FIG. 6A to FIG. 6B A top plan view of a 3.5 mm wide solder contact is shown. By increasing the size of the solder pad under the solder mask to have a 0.75 mm wide protective border area, as shown in FIG. Figure 6B As shown, the underlying and adjacent insulating substrate material is protected from thermal damage caused by laser welding.

[0030] FIG. 7A to FIG. 7B A top plan view showing electrically isolated solder contacts on a top layer of a printed circuit board, Fig. 7A The designs known in the art are shown, and Figure 7B An increased solder pad size beneath a solder mask in accordance with the present disclosure is demonstrated.

[0031] Figures 8 to 9 A top plan view of solder pads connected to traces etched into a top metal layer of a printed circuit board is shown in accordance with the subject disclosure.

[0032] Fig.10 A top plan view of the solder contact area is shown and a method of sizing the solder pad extending under the solder mask is demonstrated. DETAILED DESCRIPTION

[0033] The subject technology overcomes many prior art problems associated with printed circuit boards and laser welding. Advantages and other features of the technology disclosed herein will become more apparent to those of ordinary skill in the art from the following detailed description of certain exemplary embodiments in conjunction with the accompanying drawings, and in which the same reference numerals represent similar structural elements. It should be noted that directional indications such as vertical, horizontal, up, down, right, left, etc. are with respect to the accompanying drawings and are not intended to be used in a limiting manner.

[0034] exist Figure 1 A schematic cross-sectional view of a printed circuit board 100 is shown in FIG. The printed circuit board 100 is a multi-layer structured device that establishes electrical connections between electronic components. The layers of the printed circuit board 100 may vary, but generally consist of a base material 102 and a copper foil laminate 104.

[0035] The base material 102 consists of a glass substrate on which a flame retardant (FR) epoxy resin (such as a resin that meets the requirements of UL94V-0) is deposited and partially cured. The base material 102 is electrically insulating and provides the electrical isolation necessary for the operation of the device for the continuous metal layer. Due to its strength-to-weight ratio, waterproof properties and manufacturability, FR4 is a typical material for constructing the layer 102 of the printed circuit board 100. The material has a temperature index of 110°C to 150°C, which is the maximum use temperature at which the key property of the material will remain within acceptable limits for a long time. In one embodiment, FR4 is made of a flame retardant epoxy resin and a glass fabric composite material. In addition, FR4 has significant adhesion properties to copper foil and has minimal water absorption.

[0036] The printed circuit board 100 is also composed of alternating copper foil layers 106 and insulating layers 110. During manufacturing, heat is applied to bond together the layers 102, 106, 110. The copper foil layers 106 are electrochemically etched to define copper traces that conduct electricity and form the circuitry of the device, which are electrically connected together by vias 112.

[0037] The top copper surface 104 of the laminate is coated with a patterned solder mask 108 to define copper areas exposed for electrical connection to the board 100. Solder is used to make electrical connections between the top copper surface 104, wires (not expressly shown), and component electrical leads (not expressly shown).

[0038] The top metal layer 104 of the printed circuit board 100 has a solder contact area whose size is limited by the solder mask 108. The area of ​​the solder contact area needs to be large enough so that it contains the exposed wire length and the resulting solder joint. Sufficient heat is required to completely melt the solder without damaging the printed circuit board 102 laminate. If the solder pad is large, more time and heat will be required to fully heat the assembly to the desired temperature.

[0039] Lasers can be used to transfer heat energy to precisely located areas during the soldering process. If laser heat is applied to areas adjacent to solder pads, such as by incident laser light reflecting off the solder onto the printed circuit board 100, the base material 102 or the insulating layer 110 may be damaged. Excessive heat may cause delamination of the printed circuit board 100 or destroy the necessary insulating properties of the composite material.

[0040] For context, solder is a fusible metal alloy with a low melting temperature and low surface tension that is used to join conductive surfaces in the construction of electrical devices. Solders typically have a range of melting temperatures from 90°C to 450°C. The composition of the solder alloy determines the melting temperature. Alloys with higher or lower melting temperatures can be selected and mixed to achieve the best properties for the manufacturability of the electrical connection. A two-phase mixture of a low melting temperature alloy and a high melting temperature alloy can be selected and prepared with a flux that reduces the surface tension of the molten alloy. Depending on the application, the mixture can be prepared into a solder paste or wire.

[0041] To make an electrical connection, the two components to be connected are brought into close proximity with solder and the assembly is heated to melt the solder causing it to flow and coat the surfaces of both components. The molten solder is allowed to cool and solidify. This allows the connection to be made using electrical conductivity. The mechanical and electrical quality of the connection depends on the components reaching the proper temperature. Temperatures in excess of 200°C are typically required to melt the solder paste and form a quality connection.

[0042] FIG. 2A to FIG. 2BAn example of damage 220 caused to the printed circuit board 200 during laser welding is shown. As described above, once the insulation between two metal layers of the printed circuit board 200 is damaged, the circuit is destroyed and may cause device failure.

[0043] Reference now Figure 3 , in one aspect of the present disclosure, the solder mask 308 defines the solder contact area 304. However, the solder pad 316 extends beyond the contact area 304 exposed by the solder mask 308 to protect the underlying and adjacent substrate material and adjacent materials forming the printed circuit board 300. The extension of the solder pad 316 is referred to herein as a protective border region 318. Preferably, the protective border region 318 is disposed completely around the periphery 319 of the solder contact area 304, except for the channel 324 for receiving the conductive wire for connection to the board 300, thereby providing thermal protection in all directions relative to the solder contact area 304.

[0044] In this embodiment, if heat is applied outside the solder area 304 and applied to the edge 320 of the solder mask 308, the pad 316 absorbs the heat by virtue of the pad 316 extending below the edge 320 of the solder mask 308. Thus, the layers of the printed circuit board 300 are thermally protected. It is worth noting that in order to promote faster soldering, the amount of copper around the area of ​​the pad 304 defined by the solder mask 308 needs to be minimized, but large enough to provide protection to the printed circuit board 300 insulation layer. Fig.10 Discuss this optimization.

[0045] In addition to Figure 3 In addition to the description, Figure 4A and Figure 4B Schematic illustrations of solder pads 216 embedded on printed circuit boards 200 known in the art and solder pads 316 of the improved printed circuit board 300 design are also compared. As presented, the solder pads 316 of the improved printed circuit board 300 extend below the edge of the solder mask 308, thus protecting the layers of the improved printed circuit board 300 from incident heat during the soldering process.

[0046] Figure 5A and Figure 5B A further example comparison of a printed circuit board 200 and an improved printed circuit board 300 design known in the art is shown. Figure 5A The solder pad 216 in is 2.5 mm wide. Figure 5B As shown, solder pad 316 has an increased width of 3.5 mm, providing a 0.50 mm lateral extension of solder pad 316 below solder mask 308. In addition, the height of solder pad 316 is increased by 0.50 mm. Thus, Figure 5BA protective border region 318 is provided 0.50 mm around the periphery of the solder contact area 304 in all directions, thereby protecting the underlying and adjacent insulating base material (not expressly shown) from thermal damage caused by the laser welding performed within the contact area 304.

[0047] Fig. 6A and Figure 6B A further example comparison of a printed circuit board 200 and an improved printed circuit board 300 design known in the art is shown. Here, Fig. 6A The solder pad 216 in is 3.5 mm wide. Figure 6B As shown, solder pad 316 has an increased width of 5.0 mm, providing a 0.75 mm lateral extension of solder pad 316 below solder mask 308. In addition, the height of solder pad 316 is increased by 0.75 mm. Thus, Figure 6B A protective border region 318 is provided 0.75 mm around the periphery of the solder contact area 304 in all directions, thereby protecting the underlying and adjacent insulating base material (not expressly shown) from thermal damage caused by the laser welding performed within the contact area 304.

[0048] exist Figure 5B and Figure 6B , the width of the protective border region 318 is approximately 20% of the width of the solder contact 304. This profile factor is sufficient to provide protection to the underlying and adjacent substrate material while not being so large as to add excessive thermal mass to the assembly, thereby requiring more heating to form a quality electrical connection.

[0049] Reference now FIG. 7A to FIG. 7B , the printed circuit board 200 and the improved printed circuit board 300 known in the art are further juxtaposed in an embodiment with electrically isolated solder contacts. In this regard, the solder contacts 304 on the top layer of the printed circuit board 300 can be electrically isolated on the first metal layer of the composite structure. These isolated solder pads 316 can be connected by, for example, Figure 1 The vias are shown connected to the underlying metal layer.Nonetheless, the principles discussed herein still apply, as the solder pad 316 of the present disclosure provides a protective border region 318 disposed around the periphery of the solder contact area 304 for thermal protection.

[0050] Figures 8 to 9Various embodiments of improved printed circuit boards 300, 400 are shown having solder pads 316, 416 with protective border regions 318, 418. Solder contacts 304, 404 on the top layer of the printed circuit board 300, 400 connect to traces 322, 422 etched into the top metal layer of the printed circuit board 300, 400. Furthermore, the solder pads 316, 416 provide a protective border region 318, 418 disposed around the periphery of each solder contact area 304, 404 for thermal protection. Figures 8 to 9 The illustration further shows that in an embodiment of the present disclosure, the width of the solder pad 316, 416 can increase the width of the protection border 318, 418, and the width of the protection border is approximately the width of the exposed solder contact area 304, 404, which is independent of the trace 322, 422 and does not modify the trace.

[0051] Reference now Fig.10 , showing the solder contact area 504 of the solder pad 516 in plan view. The width W of the solder pad 516 sa This is typically determined by the size of the conductor 516 that may be soldered to a given solder pad 516. However, by selecting the size of the solder pad 516 based on how the laser soldering manufacturing process can allow heat to be concentrated outside of the solder contact area 504, an improved and more secure connection is made.

[0052] For example, the height and width (H c and W c ) to determine the minimum reflection angle θ sa , which takes into account the reflection of the laser outside the solder contact area 504 during the laser welding process. Thereafter, a supplementary angle φ (taking into account variations in part tolerances, conductor placement, and laser welding processes) can be added to θ sa To calculate the maximum reflection angle θ ep In this example, the angle φ typically ranges between 5 and 30 degrees.

[0053] Afterwards, the maximum reflection angle θ can be used ep To calculate the size W of the solder pad extension based on the equation mentioned below ep .

[0054]

[0055] 5<φ<30 degrees

[0056] Additionally, the conductor shapes used in the above calculations may be square, rectangular, or circular shapes that approximate a square. Other commercially available conductor shapes that may contain circular edges may be used in the above calculations, given their approximate width and height.

[0057] Incidentally, multiple factors contribute to achieving good quality solder connections while maintaining the layered electrical structure of the printed circuit board, including the thermal properties of the soldering process and assembly technology. These factors can include the width of copper exposed by the solder mask material (not clearly shown), or the diameter and morphology of the wire to be soldered. For example, thicker wires require more heat and solder to form a solid connection. Similarly, whether the wire is composed of a single conductor or multiple strands will also affect the process. In addition, the amount of solder or solder paste required will depend on the size of the solder contact area and the characteristics of the wire. All of these factors will determine the heat required to melt the solder and form a solid electrical connection.

[0058] Those skilled in the relevant art will appreciate that, in alternative embodiments, the functions of several elements may be performed 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 embodiments. In addition, functional elements that are shown as different for the purpose of illustration may be incorporated into other functional elements in a particular embodiment.

[0059] While the present technology has been described with respect to various embodiments, those skilled in the art will readily appreciate that various changes and / or modifications may be made to the subject technology without departing from the scope of the present disclosure.

Claims

1. A printed circuit board, comprising: Electrical insulation layer; an electrically conductive solder pad disposed at least partially over the electrically insulating layer, the electrically conductive solder pad defining a solder contact area configured for establishing an electrical connection to an electrical component by means of laser welding; as well as a solder mask coating the conductive solder pad and defining an exposed area of ​​the conductive solder pad, The conductive solder pad protects the electrically insulating layer from incident heat during the laser welding by extending a length below the solder mask along a periphery of the exposed area.

2. The printed circuit board of claim 1, wherein an extension length of the conductive solder pad depends on a height and a width of the solder contact area.

3. The printed circuit board of claim 2, wherein the extension length of the conductive solder pad is further dependent on a minimum reflection angle that accounts for laser reflection outside the solder contact area during laser soldering.

4. The printed circuit board of claim 3, wherein the extension length of the conductive solder pad is further dependent on a maximum reflection angle, the maximum reflection angle comprising the minimum reflection angle and a supplemental reflection angle that accounts for variations in part tolerances, conductor placement, and / or during laser welding.

5. The printed circuit board of claim 4, wherein the reflection angle to account for component tolerances, conductor placement, and / or variations during laser welding ranges between 5 and 30 degrees.

6. The printed circuit board of claim 1, wherein the extension length of the conductive solder pad is determined by the following equation: in: W ep is the extended length of the conductive solder pad; H c and W c are respectively the height and width of the solder contact area of ​​the conductive solder pad; θ sa is a minimum reflection angle that takes into account laser reflection outside the solder contact area during laser welding; φ is a supplemental reflection angle that accounts for part tolerances, conductor placement, and / or variations during laser welding; and W sa is the width of the conductive solder pad.

7. The printed circuit board according to claim 6, wherein Between 5 and 30 degrees.

8. The printed circuit board of claim 1, wherein the conductive solder pad is disposed completely around the periphery of the solder contact area, except for a channel in the printed circuit board for receiving a conductive trace, thereby providing thermal protection in all directions relative to the solder contact area.

9. The printed circuit board of claim 1, wherein the conductive solder pad has an extension length of 0.25 to 2.5 mm.

10. A printed circuit board, comprising: Insulation layer; a copper pad disposed over the insulating layer, the copper pad defining a solder contact area for soldering a component thereto; as well as a solder mask layer disposed over the copper pad, The copper pad extends below the solder mask layer to protect the insulating layer during soldering.

11. The printed circuit board of claim 10, wherein the extension length of the copper pad depends on the height and width of the solder contact area.

12. The printed circuit board of claim 11, wherein the extension length of the copper pad is further dependent on a minimum reflection angle that accounts for light reflection outside the solder contact area during soldering.

13. The printed circuit board of claim 12, wherein the extension length of the copper pad is further dependent on a maximum reflection angle, the maximum reflection angle comprising the minimum reflection angle and a supplementary reflection angle that takes into account variations in part tolerances, conductor placement, and / or soldering.

14. The printed circuit board of claim 13, wherein the reflection angle to account for component tolerances, conductor placement and / or variations during soldering ranges between 5 and 30 degrees.

15. The printed circuit board of claim 10, wherein the extension length of the copper pad is determined by the following equation: in: W ep is the extended length of the copper pad; H c and W c are respectively the height and width of the solder contact area of ​​the copper pad; θ sa is a minimum reflection angle that accounts for light reflection outside the solder contact area during soldering; φ is a supplemental reflection angle that accounts for part tolerances, conductor placement, and / or variations during welding; and W sa is the width of the copper pad.

16. The printed circuit board according to claim 15, wherein Between 5 and 30 degrees.

17. The printed circuit board of claim 10, wherein the copper pad extends 0.25 to 2.5 millimeters below the solder mask layer.

18. The printed circuit board of claim 10, wherein the copper pad extends beneath the solder mask layer along a periphery of the solder contact area.

19. The printed circuit board of claim 10, wherein the copper pad extends beneath the solder mask layer along a periphery of the solder contact area, except for a channel in the printed circuit board for receiving a conductive trace.

20. A method of establishing a connection on a printed circuit board, the printed circuit board comprising an electrically insulating substrate layer, the method comprising the steps of: a solder pad positioned adjacent to the electrically insulating base layer, the solder pad defining an electrical contact area; coating the solder pad with a solder mask, the solder pad extending beyond a sufficient electrical contact area and extending under the solder mask to establish a peripheral extension, the electrical contact area remaining exposed; as well as The conductive wire is laser welded to the electrical contact area using a laser, so that when light from the laser is reflected from the electrical contact area, the reflected light strikes the peripheral extension instead of the electrically insulating base layer, and thereby the electrically insulating base layer is protected from damage caused during laser welding.

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