The present invention relates to printed circuit board manufacturing, repair and modification, and to removing surface mount devices from printed circuit boards.
In a manufacturing process well known in the art of attaching surface mount devices (SMDs) to printed circuit boards (PCBs) called “solder reflow,” an SMD such as a Quad Flat Pack (QFP) IC package is soldered to a printed circuit board (PCB). Contacts disposed on the SMD are soldered onto corresponding pads disposed on the PCB that have been previously coated with solder paste. When located on the top side of the PCB, the force of gravity generally keeps an SMD in place while a PCB is heated to melt the solder and attach the SMD to the PCB.
If, however, during the heating process the PCB is oriented such that the SMD is located upside down on the bottom side of the PCB, the SMD will fall off the PCB during heating unless the SMD has first been glued to the PCB. Thereafter the SMD may be soldered to the PCB. Glue is often used in such a fashion when an SMD is to be mounted on a double-sided PCB or when a wave-solder process is employed rather than a standard solder reflow process.
There arise situations where it becomes necessary to remove an SMD from a PCB after soldering. One such situation may arise during production manufacturing where testing reveals that an SMD is defective and must be replaced. Another such situation may arise in a post-manufacturing scenario where a PCB fails in the field and is returned to the manufacturer, vendor or supplier for failure analysis. Yet another such situation may arise during IC package qualification towards the end of a PCB manufacturing process, where an SMD is removed from a PCB to determine how tolerant the SMD is to stresses induced by wave soldering. Still other circumstances arise where SMDs that have been glued and soldered to PCBs need to be removed from a PCB.
In the context of removing a soldered and glued SMD from a PCB, removing solder bonding the contacts of the SMD to PCB pads may be accomplished rather easily using well-known solder reflow and heating techniques. The glue attaching an SMD to a PCB is another matter, however. One known method of breaking the adhesive bond between an SMD AND A PCB is to remove all solder from the SMD contacts and PCB pads and then heat the glue to weaken the bond. Thereafter, the SMD may be removed from the PCB by striking, hitting, tapping or otherwise applying a suitable mechanical force to the SMD to break the adhesive bond. If the glue is heat-resistant or of a high-temperature variety, however, heating the adhesive bond may result in the adhesive bond not breaking. Additionally, striking, hitting or tweaking the SMD after the glue bond has been heated may result in damage to the SMD, in which case the object of removing the SMD in the first place may be completely thwarted (e.g., when the SMD has been removed for purposes of failure analysis or IC package qualification).
Various patents containing subject matter relating directly or indirectly to the field of the present invention include, but are not limited to, the following:
U.S. Pat. No. 4,270,260 for Method for the salvage and restoration of integrated circuits from a substrate to Krueger.
U.S. Pat. No. 4,569,473 for Apparatus for and method of desoldering and removing an integrated circuit from a mounting member and for cleaning the same to Guiliano.
U.S. Pat. No. 4,588,468 for Apparatus for changing and repairing printed circuit boards to McGinty et al.
U.S. Pat. No. 4,659,004 for Device for attaching modular electronic components to or removing them from an insulative device to Fridman.
U.S. Pat. No. 4,752,025 for Surface mount assembly repair terminal to Stach et al.
U.S. Pat. No. 4,767,047 for Desoldering device to Todd et al.
U.S. Pat. No. 5,148,969 for Component reclamation apparatus and method to Boucher et al.
U.S. Pat. No. 5,553,766 for In-situ device removal for multi-chip modules to Jackson et al.
U.S. Pat. No. 5,598,965 for Integrated circuit, electronic component chip removal and replacement system to Scheu.
U.S. Pat. No. 5,707,000 Apparatus and method for removing known good die using hot shear process to Olson et al.
U.S. Pat. No. 6,360,934 Apparatus and method for removing a soldered device from a printed circuit board to Cilia et al.
U.S. Pat. No. 6,651,322 for Method of reworking a multilayer printed circuit board assembly to Currie.
U.S. Pat. No. 6,942,137 for Die removal method and apparatus to Bolde et al.
What is needed is a method and apparatus that permits an SMD to be glued to a PCB and thereafter removed without damaging the SMD or altering the characteristics of the SMD during the soldering process, as well as a device and method that does not add significantly to the cost or complexity of the PCB manufacturing process. Upon having read and understood the Summary, Detailed Descriptions and Claims set forth below, those skilled in the art will appreciate that at least some of the methods and apparatus disclosed in the printed publications listed herein may be modified advantageously in accordance with the teachings of the present invention.
In a first embodiment of the present invention, there is provided a printed circuit board comprising a plurality of pads configured to receive surface mount device contacts thereon. The pads define a surface mount device perimeter for each surface mount device that is to be mounted on the circuit board. One or more weakened zones are positioned inside the perimeter and are configured to facilitate removal of the surface mount device from the board after the surface mount device has been attached to the board with an adhesive. The one or more weakened zones may comprise, alone or in combination, one or more through-holes, through-slots, or thinned portions. The first embodiment of the present invention may also include a surface mount device and/or an adhesive disposed between the surface mount device and the printed circuit board.
In a second embodiment of the present invention, there is provided a printed circuit board having a plurality of electronic components mounted thereon, and comprising a plurality of pads configured to receive surface mount device contacts thereon. The pads for each surface mount device that is to be mounted on the board define a surface mount device perimeter on the circuit board. One or more weakened zones are positioned inside the perimeter and are configured to facilitate removal of the surface mount device from the board after the surface mount device has been attached to the board with an adhesive. The one or more weakened zones may comprise, alone or in combination, one or more through-holes, through-slots or thinned portions. The second embodiment of the present invention may also include a surface mount device and/or an adhesive disposed between the surface mount device and the printed circuit board.
In a third embodiment of the present invention, there is provided an electronic device comprising a printed circuit board having a plurality of electronic components mounted thereon, and comprising a plurality of pads configured to receive surface mount device contacts thereon. The pads define a surface mount device perimeter for each surface mount device that is to be mounted on the printed circuit board. One or more weakened zones are positioned inside the perimeter and are configured to facilitate removal of the surface mount device from the board after the surface mount device has been attached to the board with an adhesive. The one or more weakened zones may comprise, alone or in combination, one or more through-holes, through-slots or thinned portions. The third embodiment of the present invention may also include a surface mount device and/or an adhesive disposed between the surface mount device and the printed circuit board.
In a fourth embodiment of the present invention, there is provided a method of forming weakened zones in a printed circuit board to facilitate removal of a surface mount device glued to the board, where the method comprises providing the printed circuit board and forming one or more weakened zones in the printed circuit board inside a surface mount device perimeter corresponding to each surface mount device that is to be mounted on the printed circuit board. The method may further comprise one or more of forming one or more through-holes, forming one or more through-slots and forming one or more thinned portions, providing the surface mount device, dispensing an adhesive onto the printed circuit board, placing the surface mount device on the adhesive, curing the adhesive, and/or soldering the surface mount device to the printed circuit board.
In a fifth embodiment of the present invention, there is provided a method of facilitating removal of a surface mount device that has been glued and soldered to a printed circuit board, where the printed circuit board comprises one or more weakened zones located inside a surface mount perimeter corresponding approximately to the outlines of each surface mount device that is to be mounted on the printed circuit board. The method of the fifth embodiment comprises removing solder connecting surface mount device contacts to pads located on the printed circuit board and at least one of abrading, cutting, scribing, drilling, sawing, scoring, cutting, laser cutting or weakening, laser etching, applying one or more chemical solvents, applying one or more suitable chemical catalysts, treating and etching the weakened zones of the printed circuit board to facilitate release of the surface mount device from the printed circuit board. The method of the fifth embodiment of the present invention may further comprise removing the surface mount device from the printed circuit board.
In a sixth embodiment of the present invention, there is provided a method of making a printed circuit board comprising providing a substrate, forming a plurality of electrically conductive traces on or near the substrate, forming a plurality of pads on the board, the pads approximately defining a surface mount device perimeter for each surface mount device that is to be mounted on the printed circuit board, and forming one or more weakened zones inside each surface mount perimeter. The method of the sixth embodiment of the present invention may further comprise at least one of forming one or more through-holes, forming one or more through-slots and forming one or more thinned portions, providing the surface mount device, dispensing an adhesive inside the surface mount perimeters, placing the surface mount device on the adhesive, curing the adhesive, and soldering the surface mount device to the printed circuit board.
Many combinations, adaptations, variations and permutations of the printed circuit board and surface mount device manufacturing, repair and removal methods, devices and elements disclosed herein may be made without departing from the scope of the present invention.
Numerous aspects of the various embodiments of the present invention will become apparent from the following specification, drawings and claims in which:
FIGS. 3(a) and 3(b) show a top view and corresponding cross-sectional view of one embodiment of a portion of a printed circuit board of the present invention;
FIGS. 4(a) and 4(b) show a top view and corresponding cross-sectional view of another embodiment of a portion of a printed circuit board of the present invention;
FIGS. 5(a) and 5(b) show a top view and corresponding cross-sectional view of yet another embodiment of a portion of a printed circuit board of the present invention;
FIGS. 6(a) and 6(b) show a top view and corresponding cross-sectional view of still another embodiment of a portion of a printed circuit board of the present invention;
FIGS. 7(a) and 7(b) show a top view and corresponding cross-sectional view of one alternative embodiment of a portion of a printed circuit board of the present invention;
FIGS. 8(a) and 8(b) show a top view and corresponding cross-sectional view of another alternative embodiment of a portion of a printed circuit board of the present invention;
The drawings are not necessarily to scale. Like numbers refer to like parts or steps throughout the drawings.
Set forth hereinbelow are detailed descriptions of some preferred embodiments of the present invention.
Continuing to refer to
If an SMD glued to portion 70 with glue 60 is to be removed from PCB 10 and inside perimeter portion 45, intervening material portions 50a through 50d are cut or otherwise removed to permit the SMD to be removed from PCB 10 and inside perimeter portion 45 after the SMD's contacts or leads have been heated and the solder joining such contacts or leads to pads 20a through 20d has been removed. Portion 70 of PCB 10 and glue 60 remain attached to the SMD after the SMD has been removed from PCB 10 and inside perimeter portion 45. Note that enlarged section 35 in
Referring now to
FIGS. 3(a) and 3(b) show a top view and corresponding cross-sectional view, respectively, of one embodiment of portion 70 of PCB 10 of the present invention. Enlarged section 35 in
FIGS. 4(a) and 4(b) show a top view and corresponding cross-sectional view, respectively, of another embodiment of portion 70 of PCB 10 of the present invention. Enlarged section 35 in
FIGS. 5(a) and 5(b) show a top view and corresponding cross-sectional view, respectively, of yet another embodiment of portion 70 of PCB 10 of the present invention. Enlarged section 35 in
FIGS. 6(a) and 6(b) show a top view and corresponding cross-sectional view, respectively, of still another embodiment of portion 70 of PCB 10 of the present invention. Enlarged section 35 in
FIGS. 7(a) and 7(b) show a top view and corresponding cross-sectional view, respectively, of one alternative embodiment of portion 70 of PCB 10 of the present invention. Enlarged section 35 in
FIGS. 8(a) and 8(b) show a top view and corresponding cross-sectional view, respectively, of another alternative embodiment of portion 70 of PCB 10 of the present invention. Enlarged section 35 in
Note that
Note that PCB 10 of the present invention typically, although not necessarily, includes a plurality of various electronic components mounted thereon, in addition to an SMD, the pads therefor and the one or more weakened zones. Additionally, and as noted above, the one or more weakened zones of the present invention are configured to facilitate removal of the surface mount device from the board after the surface mount device has been attached to the board with an adhesive or glue.
Note further that portion 70 may not contain electrically conductive traces for interconnecting electronic components mounted on or connected to PCB 10. Additionally, in the case where PCB 10 is a double-sided surface mount PCB, portion 70 must remain unobstructed on the bottom side of PCB 10; other components cannot be placed beneath portion 70. However, the footprint occupied by portion 70 and glue 60 is fairly small, and therefore the amount of surface area dedicated to the present invention on bottom surface 25 is negligible.
Some representative examples of SMDs suitable for use in the present invention include, but are not limited to, small-outline integrated circuits (SOICs), plastic leaded chip carriers (PLCCs), thin small-outline packages (TSOICs), shrink small-outline packages (SSOCPs), thin shrink small-outline packages (TSSOPs), quarter-size small-outline packages (QSOPs), very small outline packages (VSOPs), low-profile quad flat packages (LPQFPs), plastic quad flat-packages (PQFP), ceramic quad flat-packages (CQFPs), thin quad flat packages (TQFPs), quad flat packages (QFPs), power quad flat-packages (PQFPs), metric lead packages (MLPs) and metric quad flat packages (MQFPs).
Some representative examples of structures and materials suitable for use in PCBs of the present invention include, but are not limited to, PCBs containing electrically conductive layers separated and supported by layers of insulating material (i.e., substrates that have been laminated or glued together), PCBs containing layers electrically connected to one another by drilled holes or vias filled with an electrically conductive material, PCBs comprising blind and/or buried vias, and PCBs comprising one or more of phenolic resin, glass fiber, fiberglass, epoxy resin, epoxy, polyimide, polystyrene, cross-linked polystyrene, direct bonded copper substrates and insulated metal substrates.
Gluing in methods 100 and 200 may be effected using any of a number of suitable methods well known in the printed circuit board arts. Glues such as cyanoacrylate, epoxy, high temperature epoxy, LOCTITE, acrylic adhesives and other suitable adhesives may be employed, depending on the particular manufacturing method that is to be used. Adhesive dispensing may be accomplished using well known syringe, needle or nozzle dispensing techniques, or by using pin transfer, drop placement, stencil printing or other suitable techniques. Depending on the PCB manufacturing process that has been selected and the adhesive that is to be used, glue 60 may need to be cured or heated after glue 60 has been dispensed on portion 70 and the SMD has been placed thereon.
Solder removal may be effected using any of a number of suitable methods well known in the printed circuit board arts such as thermal heating followed by suctioning of melted solder. Desoldering techniques, tools and materials suitable for use in the present invention include, but are not limited to, desoldering braids, heat guns, vacuum plungers (solder suckers), removal alloys, removal fluxes, and/or vacuum and/or pressure pumps with specialized heater tips and nozzles
Abrading and cutting methods suitable for use in the present invention include, but are not limited to, scribing, drilling, sawing, scoring, cutting, laser cutting or weakening, cutting, and abrading, such abrading and cutting methods being applied to the one or more weakened zones in an appropriate manner. Treating or etching methods suitable for use in the present invention include, but are not limited to, laser application, applying one or more suitable chemical solvents, etching, applying one or more suitable chemical catalysts, such treating or etching methods being applied to the one or more weakened zones in an appropriate manner.
In another method of the present invention, there is provided a suitable PCB substrate. A plurality of electrically conductive traces and/or vias are formed on the substrate or another portion of the PCB. A plurality of pads are formed on the board, the pads defining an approximate surface mount device perimeter 30. Weakened zones are formed inside surface mount perimeter 30.
In still another method of the present invention, portion 70 remains glued to the bottom of the removed SMD, which in most cases will not pose any significant problems. For example, in the case where a failed SMD is being replaced, the continued adherence of portion 70 to the underside of the failed and removed SMD (which will be disposed of anyway) makes no difference. In the context of SMD failure analysis, the removed SMD may be placed in a socket which includes a cavity to accept portion 70 attached to the SMD. Certain failure analysis is destructive and includes removing a portion of the integrated circuit material to provide access to the internal integrated circuit die. Such packaging material removal is not impeded by portion 70 remaining attached to the underside of the SMD.
Many different combinations, variations, adaptations and permutations may be made respecting the methods illustrated and described herein, and yet nevertheless fall within the scope of the present invention. For example, while methods 100 and 200 illustrated in
Having read and understood the present disclosure, those skilled in the art will now understand that many combinations, adaptations, variations and permutations of known printed circuit board and surface mount device manufacturing methods and structures may be employed successfully within the scope of the present invention. Accordingly, the preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein may be employed without departing from the invention or the scope of the appended claims.
In the claims, means plus function clauses are intended to cover the structures described herein as performing the recited function and their equivalents. Means plus function clauses in the claims are not intended to be limited to structural equivalents only, but are also intended to include structures which function equivalently in the environment of the claimed combination.
All printed publications and patents referenced hereinabove are hereby incorporated by referenced herein, each in its respective entirety.