US20110154659A1 - Optimizing pcb power and ground connections for lead free solder processes - Google Patents
Optimizing pcb power and ground connections for lead free solder processes Download PDFInfo
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- US20110154659A1 US20110154659A1 US12/984,074 US98407411A US2011154659A1 US 20110154659 A1 US20110154659 A1 US 20110154659A1 US 98407411 A US98407411 A US 98407411A US 2011154659 A1 US2011154659 A1 US 2011154659A1
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- electrically conductive
- planes
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- plated
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
- H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
- H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
- H05K3/3447—Lead-in-hole components
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
- H05K2201/03—Conductive materials
- H05K2201/0332—Structure of the conductor
- H05K2201/0335—Layered conductors or foils
- H05K2201/0352—Differences between the conductors of different layers of a multilayer
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
- H05K2201/06—Thermal details
- H05K2201/062—Means for thermal insulation, e.g. for protection of parts
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
- H05K2201/09—Shape and layout
- H05K2201/09209—Shape and layout details of conductors
- H05K2201/0929—Conductive planes
- H05K2201/09309—Core having two or more power planes; Capacitive laminate of two power planes
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/40—Forming printed elements for providing electric connections to or between printed circuits
- H05K3/42—Plated through-holes or plated via connections
- H05K3/429—Plated through-holes specially for multilayer circuits, e.g. having connections to inner circuit layers
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/46—Manufacturing multilayer circuits
- H05K3/4611—Manufacturing multilayer circuits by laminating two or more circuit boards
- H05K3/4641—Manufacturing multilayer circuits by laminating two or more circuit boards having integrally laminated metal sheets or special power cores
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49117—Conductor or circuit manufacturing
- Y10T29/49124—On flat or curved insulated base, e.g., printed circuit, etc.
- Y10T29/4913—Assembling to base an electrical component, e.g., capacitor, etc.
- Y10T29/49144—Assembling to base an electrical component, e.g., capacitor, etc. by metal fusion
Definitions
- PCBs are generally used to mechanically support and electrically connect electronic components using conductive pathways, or traces etched from sheets of electrically conductive material (e.g., typically copper sheets) laminated onto a non-conductive substrate.
- a PCB populated with electronic components is referred to as a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA).
- PCA printed circuit assembly
- PCBA printed circuit board assembly
- PCBs are generally rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are much cheaper and faster for high-volume production.
- Some PCBs have trace layers inside the PCB and are called multi-layer PCBs, and may, for example, be formed by bonding together separately etched thin boards.
- Some multi-layer PCBs may include several layers (e.g., 4 layers, 12 layers, 24 layers, or more).
- the electrically conductive sheets are typically specified in terms of an amount of electrically conductive material (e.g., copper weight in ounces such as 0.5 oz, 1.0 oz, etc.), and such amount translates to the “thickness” of a given electrically conductive sheet or combined sheets (e.g. two 0.5 oz sheets are the same thickness as one 1.0 oz sheet).
- Holes are typically drilled through a PCB with tiny drill bits (e.g., made of solid tungsten carbide) and/or LASERs in order to connect components to different layers of the PCB.
- the drilling may be performed by automated drilling machines, with the placement of the holes controlled by a drill tape or a computer generated drill file.
- the drill file describes the location and size of each hole to be drilled in the PCB.
- These holes are generally referred to as “vias.” These vias are often plated with conductive material (e.g., copper or aluminum) forming annular rings, which allow the electrical and thermal connection of conductors on opposite sides of a PCB.
- PCB printed circuit board
- electronic components must be attached to the PCB to form a functional PCBA.
- PCB printed circuit board
- electronic component leads, pins or the like are inserted in PTHs in the PCB.
- SMT surface-mount technology
- the components are placed on pads or lands on the outer surfaces of the PCB.
- component leads are electrically and mechanically fixed to the PCB with molten metal solder.
- Wave soldering is a large-scale soldering process by which electronic components are soldered to a PCB to form an electronic assembly.
- the name is derived from the use of waves of molten solder to attach metal components to the PCB.
- the process uses a tank to hold a quantity of molten solder, and the components are inserted into or placed on the PCB and the loaded PCB is passed across a pumped wave or fountain of solder.
- the solder “wets” the exposed metallic areas of the board (e.g., those not protected with solder mask, a protective coating that prevents the solder from bridging between connections), creating a reliable mechanical and electrical connection.
- the process is much faster and can create a higher quality product than manual soldering of components.
- Wave soldering is used for both through-hole printed circuit assemblies and surface mount assemblies.
- a standard wave solder machine includes three zones: the fluxing zone, the preheating zone, and the soldering zone.
- An additional fourth zone, a cleaning zone, may also be used depending on the type of flux applied.
- a fluxer When a PCB enters the fluxing zone, a fluxer applies flux to the underside of the board.
- Two types of fluxers are used: a spray fluxer and a foam fluxer.
- precise control of flux quantities is required. Too little flux will cause poor joints, while too much flux may cause cosmetic or other problems. Also, as can be appreciated, the types of flux may affect the end result.
- the PCB will then enter the preheating zone.
- the preheating zone consists of convection heaters, which blow hot air onto the PCB to increase its temperature. Generally, preheating is necessary to activate the flux, and to remove any flux carrier solvents. Preheating is also necessary to prevent thermal shock, which may occur when a PCB is suddenly exposed to the high temperature of the molten solder wave.
- the tank of molten solder has a pattern of standing waves (or, in some cases, intermittent waves) on its surface.
- standing waves or, in some cases, intermittent waves
- the solder waves contact the bottom of the board, and stick to the solder pads and component leads by surface tension.
- molten solder fills the holes around the pins by capillary action. Precise control of wave height is required to ensure solder is applied to all areas but does not splash to the top of the board or other undesired areas. This process is sometimes performed in an inert gas nitrogen (N 2 ) atmosphere to increase the quality of the joints.
- N 2 inert gas nitrogen
- the thickness of a PCB increases (e.g., above 100 mils, 150 mils, 200 mils, or more) and the combined weight of the copper sheets increases (e.g., above 0.5 oz, 1.0 oz, 1.5 oz, 2.0 oz, or more), it may become more difficult to successfully fill the PTHs during the soldering process.
- One cause of the increased difficulty is that the molten solder tends to cool (“freeze”) prematurely before it has traveled from the bottom of the PCB to the top.
- the problem of premature freezing of the molten solder can be particularly acute when lead free solder is used in the soldering process. This problem can be further exaggerated in PTHs that are used for ground and power connections.
- a multilayered PCB may include several ground or power planes (e.g., 4 layers, 8 layers, 12 layers, or more) that include large sheets of copper.
- the multiple layers of copper sheets may conduct heat away from the molten solder (i.e., act as heat sinks), causing the solder to freeze prematurely and causing the PTH to be only partially filled with solder (e.g., 75% filled, 50% filled, or less).
- solder e.g., 75% filled, 50% filled, or less.
- the mechanical and electrical integrity of the solder connection may be significantly reduced or may even be ineffective.
- standards have been set to require a minimum amount of solder that fills a through hole for various components.
- the Institute for Interconnecting and Packaging Electronic Circuits (IPC) requires solder to fill at least 75% of the through hole for a signal pin and at least 50% of the through hole for a ground or power pin.
- FIGS. 1 and 2 illustrate top and cross-sectional views of a PCB 100 that includes PTH components.
- the PCB 100 is configured with a resistor 104 and an integrated circuit (IC) 106 .
- the PCB 100 includes a plurality of PTHs 110 A- 110 H that may be used to couple electronic components (e.g., the resistor 104 and the IC 106 ) from the top layer 102 of the PCB 100 to one or more conductors (not shown in FIG. 1 ) within or on the bottom surface of the PCB 100 .
- the PTHs 110 may receive component leads 105 A- 105 B, 107 A- 107 -E extending from the electronic components 104 , 106 .
- the PCB 100 may also include a plurality of metal traces (e.g., copper traces 111 ) that are operative to couple different components of the PCB 100 together.
- the component leads 105 A- 105 B, 107 A- 107 E may also be referred to herein as pins.
- FIG. 2 illustrates a cross-sectional view of a portion of the PCB 100 shown in FIG. 1 cut at the line 2 - 2 .
- the PCB 100 includes a plurality of dielectric layers 102 , 120 , 122 , 124 , 126 , 128 , 130 , 132 and 134 .
- the PCB 100 also includes a plurality of electrically conductive layers 114 A- 114 D, 116 A- 116 B, 118 A- 118 B disposed between (or outside of) the dielectric layers (e.g., the conductive and dielectric layers alternate).
- the IC 106 is coupled to the conductive layers 114 A- 114 -D (e.g., ground planes) of the PCB 100 by soldering a first pin 107 A (e.g. the ground pin) of the IC 106 to the PCB 100 using a first PTH 110 A partially filled with solder 140 .
- the IC 106 is also coupled to the conductive layers 118 A- 118 -B (e.g., power planes) of the PCB 100 by soldering a second pin 107 B (e.g. the power pin) of the IC 106 to the PCB 100 using a second PTH 110 B partially filled with solder 140 . Additional pins (not shown in FIG.
- the IC 106 may be coupled to additional conductive layers 116 A- 116 B (e.g. signal planes) of the PCB 100 by soldering the additional pins of the IC 106 received within additional PTHs (not shown in FIG. 2 ) of the PCB 100 .
- the PCB 100 may include signal planes, ground planes, or power planes that are connected to other components.
- solder 140 is used to mechanically and electrically couple the IC 106 to the PCB 100 .
- the pins 107 A- 107 B are respectively coupled via the solder 140 and the respective PTHs 110 A- 110 B to the respective conductive layers 114 A- 114 D, 118 A- 118 B.
- the conductive layers 116 A- 116 B e.g. signal planes
- 118 A- 118 B e.g., power planes
- the conductive layers 114 A- 114 D e.g. ground planes
- 116 A- 116 B e.g., signal planes
- the solder 140 only partially fills the openings of the PTHs 110 A- 110 B. This may be due to the heat sinking effects caused by the ground or power planes 114 A- 114 B and 118 A- 118 B that are coupled to conductive linings of the PTHs 110 A- 110 B. That is, during the soldering process, molten solder 140 fills the openings of the PTHs 110 A- 110 B from the bottom to the top via capillary action, losing heat in the process. If the molten solder 140 cools too rapidly, it may freeze prematurely, causing the opening in the PTHs 110 A- 110 B to be only partially filled as shown.
- the PTHs 110 A- 110 B are coupled to potentially large sheets of copper (e.g., the ground or power planes 114 A- 114 D, 118 A- 118 B) which have a high heat transfer coefficient, the heat of the molten solder 140 is dissipated rapidly through these electrical and heat conducting layers.
- the present embodiments provide apparatuses and methods that provide for enhanced connections between PTHs of multi-layer PCBs and electronic component leads, pins or the like, particularly when the components are attached to the multi-layer PCB using a lead-free solder process.
- the apparatuses and methods improve the likelihood that the PTHs are completely filled with solder thereby advantageously allowing the PCBs to exhibit high mechanical and electrical reliability.
- Complete filling of PTHs is achieved by configuring the electrically conductive layers within the multi-layer PCB stack in a manner that reduces the heat sinking effects of the layers.
- the PTHs may not directly contact all of the internal ground or power planes, so the heat sinking or heat transfer effects are reduced. This feature enables molten solder to substantially or completely fill an entire PTH before freezing.
- a multi-layer printed circuit board includes a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers, with the plurality of electrically conductive layers including power planes and ground planes.
- the multi-layer PCB further includes a first plated through-hole that extends through the multi-layer printed circuit board, with the first plated through-hole including an electrically conductive lining that forms a barrel for receiving a first lead of an electronic component.
- the multi-layer PCB also includes a second plated through-hole that extends through the multi-layer printed circuit board, with the second plated through-hole including an electrically conductive lining that forms a barrel for receiving a second lead of the electronic component.
- the plurality of electrically conductive layers is a first subset of the plurality of electrically conductive layers.
- Each layer of the first subset of the plurality of electrically conductive layers comprises a ground plane that is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole.
- Also among the plurality of electrically conductive layers is a second subset of the plurality of electrically conductive layers.
- Each layer of the second subset of the plurality of electrically conductive layers comprises a power plane that is electrically and mechanically connected to the electrically conductive lining of the second plated through-hole.
- the number of ground planes included in the first subset equals the number of power planes included in the second subset, although the number of ground planes included in the first subset may be fewer than the total number of ground planes included in the multi-layer PCB.
- a multi-layer printed circuit board includes a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers.
- the multi-layer PCB further includes a first plated through-hole extending through the multi-layer printed circuit board, with the first plated through-hole including an electrically conductive lining forming a barrel for receiving a first lead of an electronic component.
- the multi-layer PCB also includes a second plated through-hole that extends through the multi-layer printed circuit board, with the second plated through-hole including an electrically conductive lining that forms a barrel for receiving a second lead of the electronic component.
- each layer of the first subset of the plurality of electrically conductive layers comprises an amount of an electrically conductive material and is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole.
- a second subset of the plurality of electrically conductive layers is also among the plurality of electrically conductive layers.
- Each layer of the second subset of the plurality of electrically conductive layers comprises an amount of an electrically conductive material and is electrically and mechanically connected to the electrically conductive lining of the second plated through-hole.
- a total of the amounts of the electrically conductive material comprising the first subset of the plurality of electrically conductive layers is determined in accordance with a predetermined ratio to a total of the amounts of the electrically conductive material comprising the second subset of the plurality of electrically conductive layers.
- the electrically conductive layers in the first subset may, for example, be comprised of the same total amount of electrically conductive material (e.g., ounces or grams of copper) as the total amount of electrically conductive material (e.g. ounces or grams of copper) comprising the electrically conductive layers in the second subset.
- This provides the combined layers in the first subset with the same electrical conductive capacity as the combined layers in the second subset even though the total amount of electrically conductive material may be distributed among fewer, more, or the same number of layers in the first subset as in the second subset.
- a method of attaching an electronic component to a multi-layer printed circuit board includes providing a multi-layer printed circuit board that includes a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers, a first plated through-hole that extends through the multi-layer printed circuit board, with the first plated through-hole including an electrically conductive lining that forms a barrel for receiving a first lead of the electronic component, a second plated through-hole that extends through the multi-layer printed circuit board, with the second plated through-hole including an electrically conductive lining that forms a barrel for receiving a second lead of the electronic component, a first subset of the plurality of electrically conductive layers, wherein each layer of the first subset of the plurality of electrically conductive layers comprises an amount of an electrically conductive material and is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole, and a second subset of the plurality of
- the electrically conductive layers in the first subset may, for example, be comprised of the same total amount of electrically conductive material (e.g., ounces or grams of copper) as the total amount of electrically conductive material (e.g. ounces or grams of copper) comprising the electrically conductive layers in the second subset.
- This provides the combined layers in the first subset with the same electrical conductive capacity as the combined layers in the second subset even though the total amount of electrically conductive material may be distributed among fewer, more, or the same number of layers in the first subset as in the second subset.
- the method also includes positioning the first lead of the electronic component within the first plated through-hole, positioning the second lead of the electronic component within the second plated through-hole, soldering the first lead to the electrically conductive lining of the first plated through-hole to electrically couple the first electrical lead to each layer of the first subset of the plurality of electrically conductive layers, and soldering the second lead to the electrically conductive lining of the second plated through-hole to electrically couple the second electrical lead to each layer of the second subset of the plurality of electrically conductive layers.
- the soldering process that is employed may, for example, be a wave soldering process, and the solder may, for example, be lead-free solder.
- FIG. 1 illustrates a prior art multi-layer PCB configured with various electronic components including an IC.
- FIG. 2 is a cross-sectional view showing non-completely filled PTHs of the prior art multi-layer PCB of FIG. 1 .
- FIG. 3 illustrates one embodiment of a multi-layer PCB configured with various electronic components including an IC.
- FIG. 4 is a cross-sectional view showing one embodiment of a multi-layer PCB in which the PTHs are completely filled.
- FIGS. 5A-5B are cross-sectional views showing additional embodiments of a multi-layer PCB in which the PTHs are completely filled.
- FIGS. 6A-6C illustrate various exemplary electronic components that include leads, pins or the like that may be received in the PTHs of multi-layer PCBs such as shown in FIGS. 3-5B .
- FIGS. 3 and 4 illustrate top and cross-sectional views of a multi-layer PCB 300 that provides enhanced connections with electronic component leads, pins or the like, particularly when the components are attached to the PCB 300 using a lead-free solder process.
- the top view of FIG. 3 is similar to that of FIG. 1 , but as can be seen from the cross-sectional view of FIG. 4 , a number of features of the PCB 300 are present that differ from the prior PCB 100 of FIGS. 1 and 2 .
- the PCB 300 is configured with a resistor 304 and an integrated circuit (IC) 306 .
- the PCB 300 includes a plurality of plated through-holes (PTHs) 310 that may be used to couple electronic components (e.g., the resistor 304 and the IC 306 ) from the top layer 302 of the PCB 300 to one or more conductors (not shown in FIG. 3 ) within or on the bottom surface of the PCB 300 .
- the PTHs 310 may receive component leads or pins 305 A- 305 B, 307 A- 307 -E extending from the electronic components 304 , 306 .
- the PCB 300 may also include a plurality of metal traces (e.g., copper traces 311 ) that are operative to couple different components of the PCB 300 together.
- metal traces e.g., copper traces 311
- the PTHs 310 and component leads or pins 305 A- 305 B, 307 A- 307 E are illustrated with circular cross-sections, they may, in general, be of any desired cross-section (e.g., circular, rectangular, triangular, etc.).
- FIG. 4 illustrates a cross-sectional view of a portion of the PCB 300 shown in FIG. 3 cut at the line 4 - 4 .
- the PCB 300 includes a plurality of dielectric layers 302 , 320 , 322 , 324 , 326 , 328 , 330 , 332 and 334 .
- the PCB 300 also includes a plurality of electrically conductive layers 314 A- 314 D, 316 A- 316 B, 318 A- 318 B disposed between (or outside of) the dielectric layers (e.g., the conductive and dielectric layers alternate).
- the electrically conductive layers 314 A- 314 D, 316 A- 316 B, 318 A- 318 B can be made of copper, but, in general, any other electrically conductive material or combination of materials may be used (e.g. aluminum, gold, etc.).
- the dielectric layers 302 , 320 - 334 can be made of epoxy resin (e.g., FR4), polyimide, polytetrafluoroethylene (PTFE), or any other suitable dielectric material or combination of materials.
- the IC 306 is coupled to two conductive layers 314 A- 314 B (e.g., ground planes) of the PCB 300 by soldering a first pin 307 A (e.g. the ground pin) of the IC 306 to the PCB 300 using a first PTH 310 A that is completely filled with solder 340 , and the IC 306 is also coupled to two conductive layers 318 A- 318 B (e.g., power planes) of the PCB 300 by soldering a second pin 307 B (e.g. the power pin) of the IC 306 to the PCB 300 using a second PTH 310 B completely filled with solder 340 .
- a first pin 307 A e.g. the ground pin
- the IC 306 is also coupled to two conductive layers 318 A- 318 B (e.g., power planes) of the PCB 300 by soldering a second pin 307 B (e.g. the power pin) of the IC 306 to the PCB
- conductive layers 314 C- 314 D do not extend all the way to the first PTH 110 A, and are instead separated from the conductive lining of the first PTH 110 A by dielectric material.
- the first pin 307 A of the IC 306 is not coupled to ground planes 314 C- 314 D.
- the conductive layers 318 A- 318 B e.g. the power planes
- the conductive layers 318 A- 318 B coupled with the second pin 307 B have been moved up in the multi-layer PCB 300 stack. As described further hereinbelow, moving the conductive layers 318 A- 318 B coupled with the second pin 307 B into closer proximity with the conductive layers 314 A- 314 B coupled with the first pin 307 A minimizes return current loop inductance. Additional pins (not shown in FIG.
- the IC 306 may be coupled to additional conductive layers 316 A- 316 B (e.g. signal planes) of the PCB 300 by soldering the additional pins of the IC 306 received within additional PTHs (not shown in FIG. 4 ) of the PCB 300 .
- the PCB 300 may include signal planes, ground planes, or power planes that are connected to other components.
- solder 340 is used to mechanically and electrically couple the IC 306 to the PCB 300 .
- the first and second pins 307 A- 307 B are respectively coupled via the solder 340 and the conductive linings of the respective first and second PTHs 310 A- 310 B to the respective conductive layers 314 A- 314 b , 318 A- 318 B.
- the conductive layers 316 A- 316 B e.g. signal planes
- 318 A- 318 B e.g., power planes
- the conductive layers 314 A- 314 D e.g. ground planes
- 316 A- 316 B e.g., signal planes
- the solder 340 completely fills the openings of the PTHs 310 A- 310 B.
- molten solder 340 completely fills the openings of the PTHs 310 A- 310 B from the bottom to the top via capillary action without cooling too rapidly. This is because premature freezing during the soldering process is reduced or even eliminated altogether since the bottom two conductive layers 314 C- 314 D are not coupled to the PTHs 310 A- 310 B.
- By not coupling unnecessary conductive layers to the conductive linings of the PTHs undesired heat sinking effects during the soldering process are reduced.
- PCB 300 Unlike prior PCBs such as PCB 100 wherein all of the ground planes are connected to the ground pin of an electronic component in order to provide a “good ground”, all of the ground planes in the PCB 300 are not connected to the ground pin in order to adequately ground an electronic component.
- Electronic components on the PCB 300 such as the IC 306 may provide any number of functions including, for example, DC to DC power conversion. As such, when operated the IC 306 may require a specified level of current into the device. The level of expected current into the IC 306 in turn determines an amount (e.g.
- conductive material that is preferably incorporated into the PCB 300 and connected to the second pin 307 B via the conductive lining of the second plated through-hole 310 B and solder 340 in order to supply current to the IC 306 .
- lesser amounts might be acceptable at times, it may be desirable to supply power to the IC 306 using an amount of conductive material that can tolerate a maximum expected current flow drawn by the IC 306 without overheating to avoid damaging the PCB 300 .
- the desired amount of conductive material may be incorporated into a single thicker power plane, or as illustrated in FIG. 4 , divided among two or more thinner power planes (e.g. conductive layers 318 A- 318 B).
- the level of expected current out of the IC 306 determines an amount (e.g. weight in ounces or grams) of conductive material that should be incorporated into the PCB 306 and connected to the first pin 307 A via the conductive lining of the first plated through-hole 310 A and solder 340 in order to dissipate current from the IC 306 .
- the desired amount of conductive material may be incorporated into a single thicker ground plane, or as illustrated in FIG. 4 , divided among two or more thinner ground planes (e.g. conductive layers 314 A- 318 B).
- the total amount of electrically conductive material incorporated into the conductive layers 314 A- 314 B connected to the first pin 307 A of IC 306 can be specified in accordance with a ratio to the amount of electrically conductive material incorporated into the conductive layers 318 A- 318 B connected to the second pin 307 B of IC 306 .
- the appropriate ratio may be predetermined by application of Kirchhoff's Current Law. Since Kirchhoff's Current Law states that the sum of the currents into a node equals the sum of the currents from the node, such ratio will typically be 1:1 (assuming that all of the current into the IC 306 via the second pin 307 B is dissipated from the IC 306 via the first pin 307 A). When other conditions are present (e.g.
- the ratio may be different from 1:1.
- the ground and power planes have substantially the same dimensions (e.g. thickness and area) and the predetermined ratio is 1:1, then the number of ground planes that need to be connected to the first pin 307 A will equal the number of power planes connected to the second pin 307 B of the IC 306 . This is the situation illustrated in FIG.
- the power plane(s) may comprise a single thicker layer while the ground plane(s) comprise separate layers while still maintaining the predetermined ratio.
- a multi-layer PCB 500 includes a plurality of dielectric layers 502 , 520 - 532 and a plurality of electrically conductive layers 514 A- 514 D (e.g. ground planes), 516 A- 516 B (e.g. signal planes), and 518 AB (e.g. a power plane). Only one electrically conductive layer 518 AB (e.g.
- the thicker power plane is connected to the second pin 507 B of the IC 506 and two electrically conductive layers 514 A- 514 B (e.g., the ground planes) are connected to the first pin 507 A of the IC 506 .
- the combined total amount of electrically conductive material in the thinner conductive layers 514 A- 514 B is in a 1:1 ratio to the total amount of electrically conductive material in the single thicker conductive layer 518 AB.
- the ground plane(s) may comprise a single thicker layer while the power plane(s) comprise separate layers while still maintaining the predetermined ratio.
- a multi-layer PCB 550 includes a plurality of dielectric layers 502 , 520 - 532 and a plurality of electrically conductive layers 514 AB, 514 C, 514 D (e.g. ground planes), 516 A- 516 B (e.g. signal planes), and 518 A- 518 B (e.g. power planes). Only one electrically conductive layer 514 AB (e.g.
- the thicker ground plane is connected to the first pin 507 A of the IC 506 and two electrically conductive layers 518 A- 518 B (e.g., the power planes) are connected to the second pin 507 B of the IC 506 .
- the total amount of electrically conductive material in the single thicker conductive layer 514 AB is in a 1:1 ratio to the total amount of electrically conductive material in the thinner conductive layers 518 A- 518 B.
- FIGS. 6A-6C illustrate examples of various such electronic components. More specifically, FIG. 6A shows a resistor 600 ; FIG. 6B shows a transistor 602 ; and FIG. 6C shows an integrated circuit 604 (e.g. a DC to DC power converter).
- the electronic component that is connected in the optimized manner described herein may be comprised of two or more interconnected discrete and/or integrated components.
- the electrically conductive layers therein have been specifically arranged so as to minimize return current loop inductance among the electrically conductive layers 314 A- 314 B, 514 A- 514 B, 514 AB (e.g. the ground planes) connected to the first PTHs 310 A, 510 A and the electrically conductive layers 318 A- 318 B, 518 AB, 518 A- 518 B (e.g. the power planes) connected to the second PTHs 310 B, 510 B.
- the electrically conductive layers 314 A- 314 B, 514 A- 514 B, 514 AB e.g. the ground planes
- Such inductance due to current through the layers that are part of a closed loop circuit is reduced by positioning the electrically conductive layers 314 A- 314 B, 514 A- 514 B, 514 AB proximal to the electrically conductive layers 318 A- 318 B, 518 AB, 518 A- 518 B included in the second subset of the plurality of electrically conductive layers while minimizing the number of intervening electrically conductive layers that are not connected to the first and second PTHs 310 A, 510 A, 310 B, 510 B. More particularly, electrically conductive layers 314 C- 314 D, 514 C- 514 D (e.g.
- unconnected ground planes and electrically conductive layers 316 A- 316 B, 516 A- 516 B are not positioned within the stack between any of the electrically conductive layers 314 A- 314 B, 514 A- 514 B, 514 AB connected to the first PTHs 310 A, 510 A and the electrically conductive layers 318 A- 318 B, 518 AB, 518 A- 518 B connected to the second PTHs 310 B, 510 B.
- Such an arrangement of the electrically conductive layers within the multi-layer PCB stack is not required and there may be one or more intervening layers (e.g. signal planes, other ground planes and/or other power planes) when necessary in view of additional design considerations, but minimizing unconnected intervening layers may be desirable to achieve when possible.
Abstract
Apparatuses and methods that provide for enhanced connections between PTHs of multi-layer PCBs and electronic component leads, pins or the like. The apparatuses and methods improve the likelihood that the PTHs are completely filled with solder thereby advantageously allowing the PCBs to exhibit high mechanical and electrical reliability. Complete filling of PTHs is achieved by configuring the electrically conductive layers within the multi-layer PCB stack in a manner that reduces the heat sinking effects of the layers during the soldering process. In this regard, the PTHs may not directly contact all of the internal ground or power planes, so the heat sinking or heat transfer effects are reduced. This feature enables molten solder to substantially or completely fill an entire PTH before freezing.
Description
- This application is a divisional of U.S. patent application Ser. No. 12/651,150, entitled “OPTIMIZING PCB POWER AND GROUND CONNECTIONS FOR LEAD FREE SOLDER PROCESSES”, filed on Dec. 31, 2009. The disclosure of this related application is hereby incorporated into the present application.
- Printed circuit boards, or PCBs, are generally used to mechanically support and electrically connect electronic components using conductive pathways, or traces etched from sheets of electrically conductive material (e.g., typically copper sheets) laminated onto a non-conductive substrate. A PCB populated with electronic components is referred to as a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA). PCBs are generally rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are much cheaper and faster for high-volume production. Some PCBs have trace layers inside the PCB and are called multi-layer PCBs, and may, for example, be formed by bonding together separately etched thin boards. Some multi-layer PCBs may include several layers (e.g., 4 layers, 12 layers, 24 layers, or more). Among the layers, the electrically conductive sheets are typically specified in terms of an amount of electrically conductive material (e.g., copper weight in ounces such as 0.5 oz, 1.0 oz, etc.), and such amount translates to the “thickness” of a given electrically conductive sheet or combined sheets (e.g. two 0.5 oz sheets are the same thickness as one 1.0 oz sheet).
- Holes are typically drilled through a PCB with tiny drill bits (e.g., made of solid tungsten carbide) and/or LASERs in order to connect components to different layers of the PCB. The drilling may be performed by automated drilling machines, with the placement of the holes controlled by a drill tape or a computer generated drill file. The drill file describes the location and size of each hole to be drilled in the PCB. These holes are generally referred to as “vias.” These vias are often plated with conductive material (e.g., copper or aluminum) forming annular rings, which allow the electrical and thermal connection of conductors on opposite sides of a PCB.
- It is also possible with controlled-depth drilling, laser drilling, or by pre-drilling the individual sheets of the PCB before lamination, to produce holes that connect only some of the copper layers, rather than passing through the entire board. These holes are called “blind vias” when they connect an internal copper layer to an outer layer, or “buried vias” when they connect two or more internal copper layers and no outer layers. The walls of the vias, for boards with 2 or more layers, are generally plated with copper to form plated-through-holes (PTHs) that electrically connect the conducting layers of the PCB.
- After the printed circuit board (PCB) is completed, electronic components must be attached to the PCB to form a functional PCBA. In through-hole construction, electronic component leads, pins or the like are inserted in PTHs in the PCB. In surface-mount technology (SMT) construction, the components are placed on pads or lands on the outer surfaces of the PCB. In both kinds of construction, component leads are electrically and mechanically fixed to the PCB with molten metal solder.
- PTH electronic components may be attached to a PCB using a soldering technique referred to as wave soldering. Wave soldering is a large-scale soldering process by which electronic components are soldered to a PCB to form an electronic assembly. The name is derived from the use of waves of molten solder to attach metal components to the PCB. The process uses a tank to hold a quantity of molten solder, and the components are inserted into or placed on the PCB and the loaded PCB is passed across a pumped wave or fountain of solder. The solder “wets” the exposed metallic areas of the board (e.g., those not protected with solder mask, a protective coating that prevents the solder from bridging between connections), creating a reliable mechanical and electrical connection. The process is much faster and can create a higher quality product than manual soldering of components. Wave soldering is used for both through-hole printed circuit assemblies and surface mount assemblies.
- While there are many types of wave solder machines, the basic components and principles of these machines are generally the same. A standard wave solder machine includes three zones: the fluxing zone, the preheating zone, and the soldering zone. An additional fourth zone, a cleaning zone, may also be used depending on the type of flux applied.
- When a PCB enters the fluxing zone, a fluxer applies flux to the underside of the board. Two types of fluxers are used: a spray fluxer and a foam fluxer. For either flux application method, precise control of flux quantities is required. Too little flux will cause poor joints, while too much flux may cause cosmetic or other problems. Also, as can be appreciated, the types of flux may affect the end result.
- The PCB will then enter the preheating zone. The preheating zone consists of convection heaters, which blow hot air onto the PCB to increase its temperature. Generally, preheating is necessary to activate the flux, and to remove any flux carrier solvents. Preheating is also necessary to prevent thermal shock, which may occur when a PCB is suddenly exposed to the high temperature of the molten solder wave.
- The tank of molten solder has a pattern of standing waves (or, in some cases, intermittent waves) on its surface. When the PCB is moved over this tank, the solder waves contact the bottom of the board, and stick to the solder pads and component leads by surface tension. For the pins of PTH components, molten solder fills the holes around the pins by capillary action. Precise control of wave height is required to ensure solder is applied to all areas but does not splash to the top of the board or other undesired areas. This process is sometimes performed in an inert gas nitrogen (N2) atmosphere to increase the quality of the joints.
- As the thickness of a PCB increases (e.g., above 100 mils, 150 mils, 200 mils, or more) and the combined weight of the copper sheets increases (e.g., above 0.5 oz, 1.0 oz, 1.5 oz, 2.0 oz, or more), it may become more difficult to successfully fill the PTHs during the soldering process. One cause of the increased difficulty is that the molten solder tends to cool (“freeze”) prematurely before it has traveled from the bottom of the PCB to the top. The problem of premature freezing of the molten solder can be particularly acute when lead free solder is used in the soldering process. This problem can be further exaggerated in PTHs that are used for ground and power connections. The reason for this is that a multilayered PCB may include several ground or power planes (e.g., 4 layers, 8 layers, 12 layers, or more) that include large sheets of copper. The multiple layers of copper sheets may conduct heat away from the molten solder (i.e., act as heat sinks), causing the solder to freeze prematurely and causing the PTH to be only partially filled with solder (e.g., 75% filled, 50% filled, or less). When the PTH is only partially filled with solder, the mechanical and electrical integrity of the solder connection may be significantly reduced or may even be ineffective. In this regard, standards have been set to require a minimum amount of solder that fills a through hole for various components. For example, the Institute for Interconnecting and Packaging Electronic Circuits (IPC) requires solder to fill at least 75% of the through hole for a signal pin and at least 50% of the through hole for a ground or power pin.
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FIGS. 1 and 2 illustrate top and cross-sectional views of aPCB 100 that includes PTH components. The PCB 100 is configured with aresistor 104 and an integrated circuit (IC) 106. The PCB 100 includes a plurality ofPTHs 110A-110H that may be used to couple electronic components (e.g., theresistor 104 and the IC 106) from thetop layer 102 of thePCB 100 to one or more conductors (not shown inFIG. 1 ) within or on the bottom surface of thePCB 100. In this regard, the PTHs 110 may receive component leads 105A-105B, 107A-107-E extending from theelectronic components -
FIG. 2 illustrates a cross-sectional view of a portion of thePCB 100 shown inFIG. 1 cut at the line 2-2. As shown, thePCB 100 includes a plurality ofdielectric layers PCB 100 also includes a plurality of electrically conductive layers 114A-114D, 116A-116B, 118A-118B disposed between (or outside of) the dielectric layers (e.g., the conductive and dielectric layers alternate). In the example shown, theIC 106 is coupled to the conductive layers 114A-114-D (e.g., ground planes) of thePCB 100 by soldering afirst pin 107A (e.g. the ground pin) of theIC 106 to thePCB 100 using afirst PTH 110A partially filled withsolder 140. TheIC 106 is also coupled to theconductive layers 118A-118-B (e.g., power planes) of thePCB 100 by soldering asecond pin 107B (e.g. the power pin) of theIC 106 to thePCB 100 using asecond PTH 110B partially filled withsolder 140. Additional pins (not shown inFIG. 2 ) of theIC 106 may be coupled to additional conductive layers 116A-116B (e.g. signal planes) of thePCB 100 by soldering the additional pins of theIC 106 received within additional PTHs (not shown inFIG. 2 ) of thePCB 100. In this regard, thePCB 100 may include signal planes, ground planes, or power planes that are connected to other components. - As shown,
solder 140 is used to mechanically and electrically couple theIC 106 to thePCB 100. In this regard, thepins 107A-107B are respectively coupled via thesolder 140 and therespective PTHs 110A-110B to the respective conductive layers 114A-114D, 118A-118B. It is noted that the conductive layers 116A-116B (e.g. signal planes) and 118A-118B (e.g., power planes) do not contact the conductive lining of thefirst PTH 110A and are therefore not connected to thefirst pin 107A. Likewise, the conductive layers 114A-114D (e.g. ground planes) and 116A-116B (e.g., signal planes) do not contact the conductive lining of thesecond PTH 110B and are therefore not connected to thesecond pin 107B. - As shown, the
solder 140 only partially fills the openings of thePTHs 110A-110B. This may be due to the heat sinking effects caused by the ground or power planes 114A-114B and 118A-118B that are coupled to conductive linings of thePTHs 110A-110B. That is, during the soldering process,molten solder 140 fills the openings of thePTHs 110A-110B from the bottom to the top via capillary action, losing heat in the process. If themolten solder 140 cools too rapidly, it may freeze prematurely, causing the opening in thePTHs 110A-110B to be only partially filled as shown. Since thePTHs 110A-110B are coupled to potentially large sheets of copper (e.g., the ground or power planes 114A-114D, 118A-118B) which have a high heat transfer coefficient, the heat of themolten solder 140 is dissipated rapidly through these electrical and heat conducting layers. - Accordingly, the present embodiments provide apparatuses and methods that provide for enhanced connections between PTHs of multi-layer PCBs and electronic component leads, pins or the like, particularly when the components are attached to the multi-layer PCB using a lead-free solder process. The apparatuses and methods improve the likelihood that the PTHs are completely filled with solder thereby advantageously allowing the PCBs to exhibit high mechanical and electrical reliability. Complete filling of PTHs is achieved by configuring the electrically conductive layers within the multi-layer PCB stack in a manner that reduces the heat sinking effects of the layers. In this regard, the PTHs may not directly contact all of the internal ground or power planes, so the heat sinking or heat transfer effects are reduced. This feature enables molten solder to substantially or completely fill an entire PTH before freezing. Various features and embodiments are described in detail below.
- According to one aspect of the present invention, a multi-layer printed circuit board (PCB) is provided. The multi-layer PCB includes a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers, with the plurality of electrically conductive layers including power planes and ground planes. The multi-layer PCB further includes a first plated through-hole that extends through the multi-layer printed circuit board, with the first plated through-hole including an electrically conductive lining that forms a barrel for receiving a first lead of an electronic component. The multi-layer PCB also includes a second plated through-hole that extends through the multi-layer printed circuit board, with the second plated through-hole including an electrically conductive lining that forms a barrel for receiving a second lead of the electronic component. Among the plurality of electrically conductive layers is a first subset of the plurality of electrically conductive layers. Each layer of the first subset of the plurality of electrically conductive layers comprises a ground plane that is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole. Also among the plurality of electrically conductive layers is a second subset of the plurality of electrically conductive layers. Each layer of the second subset of the plurality of electrically conductive layers comprises a power plane that is electrically and mechanically connected to the electrically conductive lining of the second plated through-hole. Further, the number of ground planes included in the first subset equals the number of power planes included in the second subset, although the number of ground planes included in the first subset may be fewer than the total number of ground planes included in the multi-layer PCB.
- According to another aspect of the present invention, a multi-layer printed circuit board is provided. The multi-layer PCB includes a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers. The multi-layer PCB further includes a first plated through-hole extending through the multi-layer printed circuit board, with the first plated through-hole including an electrically conductive lining forming a barrel for receiving a first lead of an electronic component. The multi-layer PCB also includes a second plated through-hole that extends through the multi-layer printed circuit board, with the second plated through-hole including an electrically conductive lining that forms a barrel for receiving a second lead of the electronic component. Among the plurality of electrically conductive layers is a first subset of the plurality of electrically conductive layers. Each layer of the first subset of the plurality of electrically conductive layers comprises an amount of an electrically conductive material and is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole. Also among the plurality of electrically conductive layers is a second subset of the plurality of electrically conductive layers. Each layer of the second subset of the plurality of electrically conductive layers comprises an amount of an electrically conductive material and is electrically and mechanically connected to the electrically conductive lining of the second plated through-hole. Further, a total of the amounts of the electrically conductive material comprising the first subset of the plurality of electrically conductive layers is determined in accordance with a predetermined ratio to a total of the amounts of the electrically conductive material comprising the second subset of the plurality of electrically conductive layers. In this regard, the electrically conductive layers in the first subset may, for example, be comprised of the same total amount of electrically conductive material (e.g., ounces or grams of copper) as the total amount of electrically conductive material (e.g. ounces or grams of copper) comprising the electrically conductive layers in the second subset. This provides the combined layers in the first subset with the same electrical conductive capacity as the combined layers in the second subset even though the total amount of electrically conductive material may be distributed among fewer, more, or the same number of layers in the first subset as in the second subset.
- According to a further aspect of the present invention, a method of attaching an electronic component to a multi-layer printed circuit board is provided. The method includes providing a multi-layer printed circuit board that includes a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers, a first plated through-hole that extends through the multi-layer printed circuit board, with the first plated through-hole including an electrically conductive lining that forms a barrel for receiving a first lead of the electronic component, a second plated through-hole that extends through the multi-layer printed circuit board, with the second plated through-hole including an electrically conductive lining that forms a barrel for receiving a second lead of the electronic component, a first subset of the plurality of electrically conductive layers, wherein each layer of the first subset of the plurality of electrically conductive layers comprises an amount of an electrically conductive material and is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole, and a second subset of the plurality of electrically conductive layers, wherein each layer of the second subset of the plurality of electrically conductive layers comprises an amount of an electrically conductive material and is electrically and mechanically connected to the electrically conductive lining of the second plated through-hole, and wherein a total of the amounts of the electrically conductive material comprising the first subset of the plurality of electrically conductive layers is determined in accordance with a predetermined ratio to a total of the amounts of the electrically conductive material comprising the second subset of the plurality of electrically conductive layers. In this regard, the electrically conductive layers in the first subset may, for example, be comprised of the same total amount of electrically conductive material (e.g., ounces or grams of copper) as the total amount of electrically conductive material (e.g. ounces or grams of copper) comprising the electrically conductive layers in the second subset. This provides the combined layers in the first subset with the same electrical conductive capacity as the combined layers in the second subset even though the total amount of electrically conductive material may be distributed among fewer, more, or the same number of layers in the first subset as in the second subset. The method also includes positioning the first lead of the electronic component within the first plated through-hole, positioning the second lead of the electronic component within the second plated through-hole, soldering the first lead to the electrically conductive lining of the first plated through-hole to electrically couple the first electrical lead to each layer of the first subset of the plurality of electrically conductive layers, and soldering the second lead to the electrically conductive lining of the second plated through-hole to electrically couple the second electrical lead to each layer of the second subset of the plurality of electrically conductive layers. In this regard, the soldering process that is employed may, for example, be a wave soldering process, and the solder may, for example, be lead-free solder.
- In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions.
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FIG. 1 illustrates a prior art multi-layer PCB configured with various electronic components including an IC. -
FIG. 2 is a cross-sectional view showing non-completely filled PTHs of the prior art multi-layer PCB ofFIG. 1 . -
FIG. 3 illustrates one embodiment of a multi-layer PCB configured with various electronic components including an IC. -
FIG. 4 is a cross-sectional view showing one embodiment of a multi-layer PCB in which the PTHs are completely filled. -
FIGS. 5A-5B are cross-sectional views showing additional embodiments of a multi-layer PCB in which the PTHs are completely filled. -
FIGS. 6A-6C illustrate various exemplary electronic components that include leads, pins or the like that may be received in the PTHs of multi-layer PCBs such as shown inFIGS. 3-5B . -
FIGS. 3 and 4 illustrate top and cross-sectional views of amulti-layer PCB 300 that provides enhanced connections with electronic component leads, pins or the like, particularly when the components are attached to thePCB 300 using a lead-free solder process. The top view ofFIG. 3 is similar to that ofFIG. 1 , but as can be seen from the cross-sectional view ofFIG. 4 , a number of features of thePCB 300 are present that differ from theprior PCB 100 ofFIGS. 1 and 2 . - The
PCB 300 is configured with aresistor 304 and an integrated circuit (IC) 306. ThePCB 300 includes a plurality of plated through-holes (PTHs) 310 that may be used to couple electronic components (e.g., theresistor 304 and the IC 306) from thetop layer 302 of thePCB 300 to one or more conductors (not shown inFIG. 3 ) within or on the bottom surface of thePCB 300. In this regard, the PTHs 310 may receive component leads or pins 305A-305B, 307A-307-E extending from theelectronic components PCB 300 may also include a plurality of metal traces (e.g., copper traces 311) that are operative to couple different components of thePCB 300 together. Although the PTHs 310 and component leads or pins 305A-305B, 307A-307E are illustrated with circular cross-sections, they may, in general, be of any desired cross-section (e.g., circular, rectangular, triangular, etc.). -
FIG. 4 illustrates a cross-sectional view of a portion of thePCB 300 shown inFIG. 3 cut at the line 4-4. As shown, thePCB 300 includes a plurality ofdielectric layers PCB 300 also includes a plurality of electricallyconductive layers 314A-314D, 316A-316B, 318A-318B disposed between (or outside of) the dielectric layers (e.g., the conductive and dielectric layers alternate). The electricallyconductive layers 314A-314D, 316A-316B, 318A-318B can be made of copper, but, in general, any other electrically conductive material or combination of materials may be used (e.g. aluminum, gold, etc.). Thedielectric layers 302, 320-334 can be made of epoxy resin (e.g., FR4), polyimide, polytetrafluoroethylene (PTFE), or any other suitable dielectric material or combination of materials. - In the example shown, the
IC 306 is coupled to twoconductive layers 314A-314B (e.g., ground planes) of thePCB 300 by soldering afirst pin 307A (e.g. the ground pin) of theIC 306 to thePCB 300 using afirst PTH 310A that is completely filled withsolder 340, and theIC 306 is also coupled to twoconductive layers 318A-318B (e.g., power planes) of thePCB 300 by soldering asecond pin 307B (e.g. the power pin) of theIC 306 to thePCB 300 using asecond PTH 310B completely filled withsolder 340. Of note, unlike in thePCB 100 of theFIG. 1 ,conductive layers 314C-314D do not extend all the way to thefirst PTH 110A, and are instead separated from the conductive lining of thefirst PTH 110A by dielectric material. Thus, thefirst pin 307A of theIC 306 is not coupled to groundplanes 314C-314D. Further, theconductive layers 318A-318B (e.g. the power planes) coupled with thesecond pin 307B have been moved up in themulti-layer PCB 300 stack. As described further hereinbelow, moving theconductive layers 318A-318B coupled with thesecond pin 307B into closer proximity with theconductive layers 314A-314B coupled with thefirst pin 307A minimizes return current loop inductance. Additional pins (not shown inFIG. 4 ) of theIC 306 may be coupled to additionalconductive layers 316A-316B (e.g. signal planes) of thePCB 300 by soldering the additional pins of theIC 306 received within additional PTHs (not shown inFIG. 4 ) of thePCB 300. In this regard, thePCB 300 may include signal planes, ground planes, or power planes that are connected to other components. - As shown,
solder 340 is used to mechanically and electrically couple theIC 306 to thePCB 300. In this regard, the first andsecond pins 307A-307B are respectively coupled via thesolder 340 and the conductive linings of the respective first andsecond PTHs 310A-310B to the respectiveconductive layers 314A-314 b, 318A-318B. It is noted that theconductive layers 316A-316B (e.g. signal planes) and 318A-318B (e.g., power planes) are separated from the conductive lining of thefirst PTH 310A by dielectric material and are therefore not connected to thefirst pin 307A. Likewise, theconductive layers 314A-314D (e.g. ground planes) and 316A-316B (e.g., signal planes) are separated from the conductive lining of thesecond PTH 310B by dielectric material and are therefore not connected to thesecond pin 307B. - As shown, the
solder 340 completely fills the openings of thePTHs 310A-310B. During the soldering process,molten solder 340 completely fills the openings of thePTHs 310A-310B from the bottom to the top via capillary action without cooling too rapidly. This is because premature freezing during the soldering process is reduced or even eliminated altogether since the bottom twoconductive layers 314C-314D are not coupled to thePTHs 310A-310B. By not coupling unnecessary conductive layers to the conductive linings of the PTHs, undesired heat sinking effects during the soldering process are reduced. - Unlike prior PCBs such as
PCB 100 wherein all of the ground planes are connected to the ground pin of an electronic component in order to provide a “good ground”, all of the ground planes in thePCB 300 are not connected to the ground pin in order to adequately ground an electronic component. Electronic components on thePCB 300 such as theIC 306 may provide any number of functions including, for example, DC to DC power conversion. As such, when operated theIC 306 may require a specified level of current into the device. The level of expected current into theIC 306 in turn determines an amount (e.g. weight in ounces or grams) of conductive material that is preferably incorporated into thePCB 300 and connected to thesecond pin 307B via the conductive lining of the second plated through-hole 310B andsolder 340 in order to supply current to theIC 306. Although lesser amounts might be acceptable at times, it may be desirable to supply power to theIC 306 using an amount of conductive material that can tolerate a maximum expected current flow drawn by theIC 306 without overheating to avoid damaging thePCB 300. The desired amount of conductive material may be incorporated into a single thicker power plane, or as illustrated inFIG. 4 , divided among two or more thinner power planes (e.g.conductive layers 318A-318B). - By application of Kirchhoff's Current Law, it is possible to determine how much current is expected out of the
IC 306 via thefirst pin 307A. The expected amount of current out of theIC 306 via thefirst pin 307A can be used to determine the ground requirements for theIC 306. As with the power planes, the level of expected current out of theIC 306 in turn determines an amount (e.g. weight in ounces or grams) of conductive material that should be incorporated into thePCB 306 and connected to thefirst pin 307A via the conductive lining of the first plated through-hole 310A andsolder 340 in order to dissipate current from theIC 306. Although lesser amounts might be acceptable at times, it may be desirable to dissipate power from theIC 306 using an amount of conductive material that can tolerate a maximum expected current flow from theIC 306 without overheating to avoid damaging thePCB 306. The desired amount of conductive material may be incorporated into a single thicker ground plane, or as illustrated inFIG. 4 , divided among two or more thinner ground planes (e.g.conductive layers 314A-318B). - The total amount of electrically conductive material incorporated into the
conductive layers 314A-314B connected to thefirst pin 307A ofIC 306 can be specified in accordance with a ratio to the amount of electrically conductive material incorporated into theconductive layers 318A-318B connected to thesecond pin 307B ofIC 306. The appropriate ratio may be predetermined by application of Kirchhoff's Current Law. Since Kirchhoff's Current Law states that the sum of the currents into a node equals the sum of the currents from the node, such ratio will typically be 1:1 (assuming that all of the current into theIC 306 via thesecond pin 307B is dissipated from theIC 306 via thefirst pin 307A). When other conditions are present (e.g. where some current is absorbed by theIC 306 and dissipated as heat or is dissipated from theIC 306 via the additional pins of the IC 306), the ratio may be different from 1:1. When the ground and power planes have substantially the same dimensions (e.g. thickness and area) and the predetermined ratio is 1:1, then the number of ground planes that need to be connected to thefirst pin 307A will equal the number of power planes connected to thesecond pin 307B of theIC 306. This is the situation illustrated inFIG. 4 wherein only two of the four available ground planes (conductive layers 314A-314B) are connected to the power pin (first pin 307A) since only two power planes (conductive layers 318A-318B) are connected to the power pin (second pin 307B). - Referring the
FIG. 5A , the power plane(s) may comprise a single thicker layer while the ground plane(s) comprise separate layers while still maintaining the predetermined ratio. Such a situation is illustrated inFIG. 5A in which amulti-layer PCB 500 includes a plurality ofdielectric layers 502, 520-532 and a plurality of electricallyconductive layers 514A-514D (e.g. ground planes), 516A-516B (e.g. signal planes), and 518AB (e.g. a power plane). Only one electrically conductive layer 518AB (e.g. the thicker power plane) is connected to thesecond pin 507B of theIC 506 and two electricallyconductive layers 514A-514B (e.g., the ground planes) are connected to thefirst pin 507A of theIC 506. In the embodiment ofFIG. 5A , the combined total amount of electrically conductive material in the thinnerconductive layers 514A-514B is in a 1:1 ratio to the total amount of electrically conductive material in the single thicker conductive layer 518AB. - Referring the
FIG. 5B , the ground plane(s) may comprise a single thicker layer while the power plane(s) comprise separate layers while still maintaining the predetermined ratio. Such a situation is illustrated inFIG. 5B wherein amulti-layer PCB 550 includes a plurality ofdielectric layers 502, 520-532 and a plurality of electrically conductive layers 514AB, 514C, 514D (e.g. ground planes), 516A-516B (e.g. signal planes), and 518A-518B (e.g. power planes). Only one electrically conductive layer 514AB (e.g. the thicker ground plane) is connected to thefirst pin 507A of theIC 506 and two electrically conductive layers 518A-518B (e.g., the power planes) are connected to thesecond pin 507B of theIC 506. In the embodiment ofFIG. 5B , the total amount of electrically conductive material in the single thicker conductive layer 514AB is in a 1:1 ratio to the total amount of electrically conductive material in the thinner conductive layers 518A-518B. - Although the optimization of power and ground connections within a multi-layer PCB has been specifically illustrated in the context of an integrated circuit, optimization of power and ground connections can be applied to any electronic components that include leads, pins or the like that may be coupled to a PCB using PTHs.
FIGS. 6A-6C illustrate examples of various such electronic components. More specifically,FIG. 6A shows aresistor 600;FIG. 6B shows atransistor 602; andFIG. 6C shows an integrated circuit 604 (e.g. a DC to DC power converter). In addition to such discrete and single integrated components, the electronic component that is connected in the optimized manner described herein may be comprised of two or more interconnected discrete and/or integrated components. - Another feature of note with the
multi-layer PCBs FIGS. 3-5B , is the arrangement of the electrically conductive layers within the multi-layer PCB stack. In this regard, the electrically conductive layers therein have been specifically arranged so as to minimize return current loop inductance among the electricallyconductive layers 314A-314B, 514A-514B, 514AB (e.g. the ground planes) connected to thefirst PTHs conductive layers 318A-318B, 518AB, 518A-518B (e.g. the power planes) connected to thesecond PTHs conductive layers 314A-314B, 514A-514B, 514AB proximal to the electricallyconductive layers 318A-318B, 518AB, 518A-518B included in the second subset of the plurality of electrically conductive layers while minimizing the number of intervening electrically conductive layers that are not connected to the first andsecond PTHs conductive layers 314C-314D, 514C-514D (e.g. unconnected ground planes) and electricallyconductive layers 316A-316B, 516A-516B (e.g. signal layers) are not positioned within the stack between any of the electricallyconductive layers 314A-314B, 514A-514B, 514AB connected to thefirst PTHs conductive layers 318A-318B, 518AB, 518A-518B connected to thesecond PTHs - While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character. For example, certain embodiments described hereinabove may be combinable with other described embodiments and/or arranged in other ways (e.g., process elements may be performed in other sequences). Accordingly, it should be understood that only the preferred embodiment and variants thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.
Claims (20)
1. A method of attaching an electronic component to a multi-layer printed circuit board, the method comprising:
providing a multi-layer printed circuit board that includes:
a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers, the plurality of electrically conductive layers including a first group of a planes and a second group of planes;
a first plated through-hole that extends through the multi-layer printed circuit board, the first plated through-hole including an electrically conductive lining that forms a barrel for receiving a first lead of the electronic component; and
a second plated through-hole that extends through the multi-layer printed circuit board, the second plated through-hole including an electrically conductive lining that forms a barrel for receiving a second lead of the electronic component;
wherein each of the first group of planes comprises an amount of an electrically conductive material, and wherein at least one of the first group of planes is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole; and
wherein each of the second group of planes comprises an amount of an electrically conductive material, wherein at least one of the second group of planes is electrically and mechanically connected to the electrically conductive lining of the second plated through-hole, and wherein a ratio of the total amount of electrically conductive material of the at least one of the first group of planes that is electrically and mechanically connected to the electrically conductive lining of the first plated through-hole to the total amount of electrically conductive material of the at least one of the second group of planes that is electrically and mechanically connected to the electrically conductive lining of the second plated through-hole is substantially 1:1;
positioning the first lead of the electronic component within the first plated through-hole;
positioning the second lead of the electronic component within the second plated through-hole;
soldering the first lead to the electrically conductive lining of the first plated through-hole; and
soldering the second lead to the electrically conductive lining of the second plated through-hole.
2. The method of claim 1 , wherein the soldering the first lead step and soldering the second lead step respectively comprise:
electrically coupling the first lead to the at least one of the first group of planes; and
electrically coupling the second lead to the at least one of the second group of planes.
3. The method of claim 1 , wherein the soldering the first lead step and the soldering the second lead step respectively comprise:
filling a substantial entirety of the first plated through-hole with solder; and
filling a substantial entirety of the second plated through-hole with solder.
4. The method of claim 1 , wherein each of the soldering the first lead step and the soldering the second lead step comprises:
performing a wave soldering process.
5. The method of claim 1 wherein the first group of planes comprises a set of ground planes and wherein the second group of planes comprises a set of power planes.
6. The method of claim 1 wherein at least one of the first group of planes is free of electrical and mechanical connections to the electrically conductive lining of the first plated through-hole.
7. The method of claim 1 wherein the number of the at least one of the first group of planes equals the number of the at least one of the second group of planes.
8. The method of claim 1 further comprising:
arranging the plurality of electrically conductive layers in the multi-layer printed circuit board to minimize return current loop inductance among the electrically conductive layers included in the first and second groups of planes.
9. The method of claim 1 , further comprising:
selecting the at least one of the first group of planes to be positioned within the multi-layer printed circuit board proximal to the at least one of the second group of planes with a minimum number of intervening electrically conductive layers that are free of electrical connections to the electrically conductive lining of the first or second plated through-holes.
10. A method of attaching an electronic component to a multi-layer printed circuit board (PCB), the method comprising:
positioning a first lead of an electronic component into a first plated through-hole of a PCB;
positioning a second lead of the electronic component into a second plated through-hole of the PCB;
soldering the first lead to an electrically conductive barrel of the first plated through-hole so that the first lead is electrically coupled to a first subset of a group of electrically conductive ground planes of the PCB and is free of electrical connections to a second subset of the group of electrically conductive ground planes of the PCB; and
soldering the second lead to an electrically conductive barrel of the second plated through-hole.
11. The method of claim 10 , wherein the soldering the second lead step comprises:
electrically coupling the second lead to at least one of a group of electrically conductive power planes of the PCB.
12. The method of claim 11 , wherein the first subset of the group of electrically conductive ground panels and the at least one of the group of electrically conductive power planes are free from the second subset of the group of electrically conductive ground panels being positioned therebetween.
13. The method of claim 10 , wherein the positioning a first lead step comprises:
inserting the first lead from a first to a second side of the PCB, wherein first subset is positioned proximate the first side of the PCB.
14. The method of claim 13 , wherein the second subset of the group of electrically conductive ground panels is positioned proximate the second side of the PCB.
15. The method of claim 13 , wherein the second subset of the group of electrically conductive ground panels is free from an overlapping relationship with the first subset of the group of electrically conductive ground panels.
16. The method of claim 13 , wherein the soldering steps utilize lead-free solder.
17. A method of constructing a multi-layer printed circuit board (PCB), comprising:
bonding together a plurality of electrically conductive layers with dielectric material disposed between the electrically conductive layers, the plurality of electrically conductive layers including a group of ground planes and a group of power planes;
forming a plurality of vias through at least some of the plurality of electrically conductive layers; and
plating each of the vias with electrically conductive material to form a plurality of electrically conductive barrels; wherein after the plating step, a first subset of one of the group of ground planes or group of power planes is electrically connected to the electrically conductive barrel of a first of the vias and a second subset of the one of the group of ground planes or group of power planes is free of electrical connections to the electrically conductive barrel of the first via.
18. The method of claim 17 , further comprising:
inserting a lead of an electrical component into the first via; and
soldering the lead to the electrically conductive barrel of the first via.
19. The method of claim 18 , wherein the soldering step comprises:
performing a wave soldering process.
20. The method of claim 19 , wherein the performing step comprises:
filling a substantial entirety of the first via with a lead-free solder.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US12/984,074 US20110154659A1 (en) | 2009-12-31 | 2011-01-04 | Optimizing pcb power and ground connections for lead free solder processes |
Applications Claiming Priority (2)
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US12/651,150 US7902465B1 (en) | 2009-12-31 | 2009-12-31 | Optimizing PCB power and ground connections for lead free solder processes |
US12/984,074 US20110154659A1 (en) | 2009-12-31 | 2011-01-04 | Optimizing pcb power and ground connections for lead free solder processes |
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US12/651,150 Division US7902465B1 (en) | 2009-12-31 | 2009-12-31 | Optimizing PCB power and ground connections for lead free solder processes |
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US12/651,150 Active US7902465B1 (en) | 2009-12-31 | 2009-12-31 | Optimizing PCB power and ground connections for lead free solder processes |
US12/984,074 Abandoned US20110154659A1 (en) | 2009-12-31 | 2011-01-04 | Optimizing pcb power and ground connections for lead free solder processes |
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US20140183550A1 (en) * | 2012-12-31 | 2014-07-03 | Efficient Power Conversion Corporation | Parasitic inductance reduction for multilayered board layout designs with semiconductor devices |
DE102020208214A1 (en) | 2020-07-01 | 2022-01-05 | Zf Friedrichshafen Ag | Circuit board, inverter, motor vehicle and method for producing a circuit board |
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JP2008227272A (en) * | 2007-03-14 | 2008-09-25 | Fujitsu Ltd | Printed wiring board and electronic apparatus |
US20100236823A1 (en) * | 2009-03-18 | 2010-09-23 | Sun Microsystems, Inc. | Ring of power via |
CN103379727A (en) * | 2012-04-26 | 2013-10-30 | 鸿富锦精密工业(深圳)有限公司 | Circuit board with electrostatic protection structure |
JP7000964B2 (en) * | 2018-03-30 | 2022-01-19 | 株式会社デンソー | Multi-layer transmission line |
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Cited By (8)
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US20140183550A1 (en) * | 2012-12-31 | 2014-07-03 | Efficient Power Conversion Corporation | Parasitic inductance reduction for multilayered board layout designs with semiconductor devices |
US9035417B2 (en) * | 2012-12-31 | 2015-05-19 | Efficient Power Conversion Corporation | Parasitic inductance reduction for multilayered board layout designs with semiconductor devices |
KR20150102983A (en) * | 2012-12-31 | 2015-09-09 | 이피션트 파워 컨버젼 코퍼레이션 | Parasitic inductance reduction circuit board layout designs for multilayered semiconductor devices |
CN105075405A (en) * | 2012-12-31 | 2015-11-18 | 宜普电源转换公司 | Parasitic inductance reduction circuit board layout designs for multilayered semiconductor devices |
KR102151200B1 (en) | 2012-12-31 | 2020-09-03 | 이피션트 파워 컨버젼 코퍼레이션 | Parasitic inductance reduction circuit board layout designs for multilayered semiconductor devices |
DE102020208214A1 (en) | 2020-07-01 | 2022-01-05 | Zf Friedrichshafen Ag | Circuit board, inverter, motor vehicle and method for producing a circuit board |
US20220007505A1 (en) * | 2020-07-01 | 2022-01-06 | Zf Friedrichshafen Ag | Printed circuit board, inverter, motor vehicle and method for producing a printed circuit board |
US11956895B2 (en) * | 2020-07-01 | 2024-04-09 | Zf Friedrichshafen Ag | Printed circuit board, inverter, motor vehicle and method for producing a printed circuit board |
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