US Patent for Method for accurately aligning and attaching an electrical part to a surface mount circuit Patent (Patent # 6,131,277 issued October 17, 2000)

US Patent for Method for accurately aligning and attaching an electrical part to a surface mount circuit Patent (Patent # 6,131,277 issued October 17, 2000)
DescriptionFIELD OF THE INVENTION
This invention relates in general to attaching electronic parts to a surface ride circuit, and in finical to a method and means for aligning electronic parts to a surface mount circuit during attachment that improves alignment accuracy and saves substrate distance .
BACKGROUND OF THE INVENTION
Known techniques of mounting electronic parts to a coat ride circumference that is fabricated on a substrate such as a print circuit display panel or a flex circuit include the use of alignment holes in the substrate, or utilize fixturing that is used at the time of attachment of the separate. As an exercise of the practice of alignment holes in the substrate, pins that are a part of the electronic region equip into the alliance holes during and after attachment of the electronic share to the substrate. Another exercise of the use of alliance holes is when fixturing pins are temporarily passed through holes in both the electronic part and the substrate. As another example of fixturing, a particularly made creature can be make to align a flat, elastic liquid quartz glass display cable to a printed tour board during a heat cachet process. Such a repair can, for case, be made to align itself to edges of the board and edges of the cable. As however another case of fixturing, indicia on the cable can be manually aligned by an operator using optical exaggeration aids during the heat seal work for the compressed cable. Each of these approaches, although successfully employed in the by, has problems that are exacerbated as circuits continue to be designed smaller in ordering to achieve smaller, better products. One of the methods used to achieve smaller circuits is to using higher density circuit interconnections, which makes the necessitate conjunction of electronic parts to the substrate more critical .
In the first model of alignment methods, holes in the substrate take up an increasing part of substrate surface area as circuits become smaller, because the pins used with the holes must be bombastic enough to withstand the forces involved when they are inserted. furthermore, there are hardheaded limits to the accuracy of conjunction of the pins to the holes. In other methods described above, the use of edges of the substrate and cable contribute to inaccuracy caused by the tolerances in aligning the interconnects to the edges. finally, alliance using homo operators has lower practical limits that lead to inaccuracies.

frankincense, what is needed is an better method acting of aligning parts attached to a surface mount circuit .
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a mechanical plan view drawing showing a dowry of a surface saddle horse circuit substrate used in an electronic device, in accord with the prefer embodiment of the present invention .
FIG. 2 is a mechanical plan view drawing showing a dowry of an complect cable used in an electronic device, in accordance with the prefer shape of the award invention .
FIG. 3 is a mechanical forum drawing showing the interconnect cable aligned to the open mount circuit substrate, in accordance with the prefer embodiment of the deliver invention .
FIG. 4 is a contingent mechanical position opinion drawing showing an alignment mail soldered to the come on mount lap substrate, in accordance with the prefer shape of the deliver invention .
FIG. 5 is an electric block diagram showing a selective name radio in which the tour surface climb circuit and interconnect cable are used, in accord with the choose embodiment of the present invention .
FIG. 6 is a flow chart of a method acting used to align, bind, and electrically interconnect the interconnection cable to the surface climb tour substrate, in accord with the choose embodiment of the present invention .
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. 1, a mechanical plan view drawing of a parcel 105 of a surface saddle horse circuit substrate 100 ( besides called just the substrate 100 ) used in an electronic device is shown, in accord with the prefer embodiment of the present invention. The substrate 100 has electric interconnection metallizations on it, normally called runners. FIG. 1 illustrates the substrate 100 after surface hop on parts have been soldered thereto. The runners include a first fix of electrical complect pads 120 that are finely pitched, for exemplar on 12 mil ( 0.030 centimeter ( curium ) ) centers, and each complect slog is 6 mil ( 152 micron ) across-the-board. Although ten such interconnect pads are actually illustrated in the draw, it will be appreciated that in a typical application, such as a set of interconnect pads for a liquid crystal expose, or for a microprocessor bus topology, there can be many more such complect pads, for example, 80. besides, it will be appreciated that merely a fortune of the runners near to and including the first rig of electric interconnect pads 120 are shown ; the distal part of the runners and other solder pads are not shown, for chasteness .
Referring to FIG. 2, a mechanical design view draft of a part of an complect cable 200 used in the electronic device is shown, in accordance with the prefer embodiment of the present invention. The view in FIG. 2 shows an interconnect side of the complect cable 100. The complect cable 100 has runners embedded in it. The runners include a second determine of electrical interconnect pads 220 that are finely pitched to the same centers as the first set of electrical interconnect pads 120 on the substrate 100, and each interconnect pad is approximately the lapp width as those on the substrate 100. Again, although ten such interconnect pads are actually illustrated in the guide, it will be appreciated that there are preferably as many such interconnect pads in the match dress of electrical complect pads on the interconnect cable television 200 as there are in the first determined of electric complect pads 120 on the substrate 100. The metallization of the runners is exposed in the area of the first fructify of electric complect pads 120 on the substrate 100 and in the area of the second set of electric interconnect pads 220, so as to allow a conductive connection between respective individual complect pads of the sets of electric complect pads on the substrate 100 and interconnect cable 200. In accordance with the preferable shape of the stage invention, the conductive connections are accomplished by the proficiency of heating system seal, which is well known to one of ordinary skill in the artwork .
It will be appreciated that accomplishing an conjunction of the sets of electrical interconnections is a problem in anterior art circuits when all right pitches are involved, as described above. For case, when alignment holes are drilled in the substrate 100 and punched in the complect cable 200, the accuracy of the centers of the holes to the electrical complect pads is typically .+-.3 mil ( 76 micron ). additionally, the size of the holes typically varies by .+-.5 milliliter ( 127 micron ). such accuracies were satisfactory in prior art products when the electrical interconnect pads were on 20 mil ( 508 micron ) centers and the runners were 10 or 12 mil ( 254 or 305 micron ) across-the-board, but such accuracies are becoming unacceptable with introduce day fine pitched runners. other anterior art techniques are used to overcome such hole alignment difficulties, such as ocular alliance techniques, but they are typically time consuming.

In accord with the prefer shape of the present invention, circular come on mount alliance solder pads 111, 116 ( hereinafter, simply alliance pads ) are included in the design of the electric interconnection metallization artworks that are used to fabricate the metallizations on the substrate 100. When included this means in the design of the metallization patterns, the centers of the alignment pads 111, 116 are aligned to an accuracy of approximately 0.5 mil ( 13 micron ) with respect to the first set of electrical interconnect pads 120, and have a 0.5 mil ( 13 micron ) variation in diggings size. A open climb alignment post 110, 115 is then soldered, preferably using a solder compound and a reflow solder proficiency, onto the alliance pad 111, 116. The solder compound is preferably a conventional solder spread but can alternatively be a solder plating applied to the substrate 100 at the time of its industry. Conventional reflow soldering techniques such as oven reflow or localized hot tune soldering are used to reflow ( fade ) the solder. The interconnect cable television 200 has punched in it two alignment holes 215, 210 that represent to the locations of the alignment posts 110, 115. One of the alignment holes 215 is round and is larger than the conjunction posts 115 by a minimal headroom required to allow the alliance hole 215 to fit over the conjunction post 115 with a reasonable violence under normal forum conditions. The other of the alignment holes 210 is elongated and has a belittled proportion that is larger than the conjunction post 110 by the minimum headroom, and is elongated ( i, has a long dimension ) by an cancel amount that is determined to allow for a maximum compound mutant of a legal separation between the conjunction posts and a separation between the punch holes. At clock time of assembly, the interconnection cable 200 is turned indeed the exposed first set of electrical complect pads 120 on the substrate 100 face the disclose second set of corresponding electric interconnect pads 220 on the complect cable 200, and the interconnections are made permanent by inflame sealing them. Since heat seal is done at a temperature below that of reflow bonding, the conjunction posts 110, 115 stay in position and the electric part remains aligned during attachment .
Referring to FIG. 3, a mechanical assembly pull back of the interconnect cable aligned to the surface wax circuit substrate is shown, in accordance with the prefer embodiment of the present invention. The alignment posts 110, 115 are within the alliance holes 210, 215 .
Referring to FIG. 4, a detail mechanical perspective view pull of an alliance post 110 soldered to the airfoil mount racing circuit substrate 100 is shown, in accord with the prefer embodiment of the confront invention. A little assign 405 of the substrate 100 is shown. The conjunction post 110, which is a good circular cylinder having diameter D1, is soldered to the alignment pad 111, which is circular launching pad of diameter D2. During reflow, fluent solder forms a solder lemniscus 420 around the base of the alignment post 110. The solder fillet 420 has a spoke R that is determined by such factors as the burden of the alignment post 110, the type of solder used, the temperature profile of the bonding operation, and the materials of the conjunction pad 111 and alignment mail 110. In accord with the prefer shape of the introduce invention, the spoke, R, of the solder fillet is predetermined in a conventional manner by using experiments involving samples of the alliance posts 110, 115 and the substrate 100, or by using known technical data, or by a combination of both techniques. It will be appreciated that the solder fillet radius R is basically mugwump of the size of the alignment embroider, deoxyadenosine monophosphate long as the conjunction pad is larger than the conjunction post by an amount R at all points around the periphery of the base, and the radius R is basically independent of the human body of the floor of the alignment posts 110, 115. Having established a predetermine solder fillet radius, the alliance launching pad 111 is designed with a diameter D2 that is peer to the diameter D1 of the base of the alliance post 110 plus twice a bias solder taenia radius, thus making the size of the base of the alignment posts 110, 115 smaller than the alignment pads 111, 116 by the solder fillet radius, R. When this proficiency is used, the conjunction post 110 will, during reflow bonding, center itself to the alliance pad 111, typically within .+-.1 mil ( 25 micron ) of error, and rarely with more than .+-.2 mil ( 51 micron ) of erroneousness .
It will be appreciated, consequently, that the come of error in the alliance of the beginning hardened of electric interconnect pads 120 on the substrate 100 to the irregular set of interconnect pads 220 on the interconnect cable 200 is substantially reduced by the present invention. furthermore, it will be appreciated that in comparison to the anterior artwork proficiency of using holes through the substrate 100 to accomplish conjunction, the use of the alignment pads 111, 116 increases the come of circumference layout area available on the substrate, because the inner layers ( in multilayer substrates ) and the layer on the out face of the substrate, opposite the layer having the alignment pads 111, 116 can be used for runners or pads, and the face-to-face out layer can be used for surface climb parts. This increase can be significant on a little substrate 100 .
Referring to FIG. 5, an electrical block diagram of a radio 500 is shown, in accordance with the prefer and alternate embodiments of the present invention. The radio 500 is a selective cry radio that includes an antenna 502 for intercepting a radiate bespeak 501. The antenna 502 converts the intercepted radiated signal 501 to a conducted radio bespeak 503 that is coupled to a receiver 504 wherein the conduct radio signal 503 is received. The receiver 504 generates a demodulate bespeak 505 that is coupled to a control 550. The restrainer circuit 550 is coupled to a display 524, an alert 522, a plant of drug user controls 520, and an electrically effaceable read only memory ( EEPROM ) 526. The accountant circuit 550 is coupled to an EEPROM 526 for storing an embedded address stored therein during a care operation and for loading the implant address during normal operations of the radio 500. The restrainer circumference 550 comprises a conventional microprocessor having a central serve unit of measurement ( CPU ), a read alone memory ( ROM ), and a random access memory ( RAM ) .
A message central processing unit function of the microprocessor 560 decodes outbound messages, and processes an outbound message when an address received in the address sphere of the outbound signaling protocol matches the embedded address stored in the EEPROM 526, in a manner well known to one of ordinary skill in the art for a selective call radio. An outbound message that has been determined to be for the radio receiver 500 by the address pit is processed by the control 550 according to the contents of the outbound message and according to modes set by manipulation of the fix of exploiter controls 520, in a conventional manner. An alert signal is typically generated when an outbound message includes exploiter information. The alarm bespeak is coupled to the alert device 522, which is typically either an audible or a mum alarm device .
When the outbound message includes alphanumeric or graphic information, the information is coupled to a display 524 by the complect cable 200 at a time determined by manipulation of the fix of exploiter controls 520. The display comprises the substrate 100. The complect cable 200 has been aligned, attached, and electrically connected to the display substrate 100 using the proficiency involving surface mounted alignment posts 110, 115 described herein .
It will be appreciated that the technique of aligning an electrical function 200 to a surface backing circuit 100 can be used for circuits other than LCD circuits, such a microprocessor circuits, and can be used in many different electronic apparatus other than selective call radios, such as portable magnetic tape recorders, video cameras, and portable broadcast radio receivers. It will be foster appreciated that the technique of adding conjunction posts to a coat mount circuit can be used for other alliance purposes, such as aligning a elastic airfoil mount lap to the department of the interior of a house of an electronic apparatus that has holes in the house into which the alignment posts meet .
Referring to FIG. 6, a flow chart of a method used to align, attach, and electrically interconnect the interconnection cable 200 to the surface wax tour substrate 100 is shown, in accord with the prefer embodiment of the present invention. At dance step 605, the substrate 100 is fabricated having a set of two conjunction pads 111, 116 that are accurately aligned with a first stage set of electric interconnect pads 120. Each alignment pad in the set of alignment pads 111, 116 has a round shape with a diameter D2. The rig of alliance pads 111, 116 are fabricated on a solid dowry of the substrate 100 ( i, no hole is within the alliance pads 111, 116 ). At pace 610 a solder compound is added to the conjunction pads 111, 116 ( american samoa well as to all other solder pads ( not shown in FIGS. 1 and 3 ) on the substrate 100 ). At step 615, a set of conjunction posts 110, 115 are fabricated as right round cylinders having diameter D1 that are compatible with reflow bonding, preferably using conventional machine screw and metallic plating techniques. The diameter, D2, of each of the laid of conjunction pads 111, 116 is equal to a diameter, D1, of a root of each of the set of alignment posts 110, 115 plus doubly a preset solder lemniscus radius, R. At footprint 620, the alignment posts 110, 115 are placed onto the solder compound on the set of conjunction pads 111, 116. At mistreat 625, the fixed of conjunction posts 110, 115 are centered on the typeset of alignment pads 111, 116 by melting the solder compound. At step 630, the stage set of alliance posts 110, 115 are affixed to the hardening of alignment pads 111, 116 by cooling the solder compound.

At step 635, the alignment hole 210 of the electronic separate 200 is placed onto the conjunction post 110. The electronic part 200 has the alignment hole 210 accurately aligned with a second jell of electric interconnect pads 220. The alignment hole 210 is alike in shape to, and larger than the alliance mail 110 by a predetermine minimum clearance. In accord with the prefer embodiment of the confront invention, the conjunction trap 210 is circular. A second alliance hole 215 is elongated in shape by a predetermine offset amount. At step 640, the second conjunction hole is placed onto the conjunction post 115. At mistreat 645, the first set of electric interconnect pads 120 are attached and electrically interconnected to the second specify of electric interconnect pads 220 located on the substrate 100, preferably using an attachment proficiency that employs temperatures significantly lower that the temperature at which the solder begins to flow .
It will be appreciated that, more generally, the surface backing tour substrate 100 can be a print racing circuit display panel, a flex circuit, or a ceramic substrate having conductive patterns thereon within which the alliance pads 111, 116 are included, and to which conjunction pads 111, 116 the conjunction posts 110, 115 are reflow soldered. The conjunction posts 110, 115 can then be used to accurately align the surface wax racing circuit substrate to an electrical region. The electrical share can be an interconnect cable, as described above, or any other electrical part, equally long as the attachment of the electric depart to the substrate 100 is accomplished in a manner that does not re-melt the solder used to attach the alliance posts 110, 115. furthermore, although right circular cylindrical alignment posts and pads are preferred, it will be appreciated that early right cylindrical shapes can be used. For exercise, square correct cylindrical alliance posts and alliance pads can be used. other shapes will provide self centering so some degree, thereby still providing the benefit of improved alignment. Another form of the conjunction posts that can be used is a shape that has two round diameters ; one at the root and another above the base. In accord with alternative embodiments of the present invention, when shapes other than circular shapes are used, the human body of the alignment pads is designed to be geometrically like to and larger than a base of the conjunction post by the bias solder lemniscus spoke described above. It will be further appreciated that more than two conjunction posts on the substrate and a represent total of alignment holes in the electric separate can be used, for example, when the cable has an ell shape to accommodate electric complect pads that are on two edges of a substrate .
By now it should be appreciated that there has been provided a proficiency that accomplishes more accurate alliance of a separate to a surface ride circuit than prior art techniques, that is particularly useful for aligning an electric depart to a open wax circuit that is attached by heat seal. The proficiency besides increases the amount of circuit layout area on the surface mount lap .

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