CA1131746A

CA1131746A - Circuit board with mounted components and method for manufacture

Info

Publication number: CA1131746A
Application number: CA322,462A
Authority: CA
Inventors: Fritz Stahl
Original assignee: Kollmorgen Technologies Corp
Current assignee: Kollmorgen Technologies Corp
Priority date: 1978-02-28
Filing date: 1979-02-28
Publication date: 1982-09-14
Also published as: JPS58103163U; IL56306A; JPS639396B2; AU4445479A; IT7947865A0; DE2809013C2; AU531356B2; SE443276B; DK152480B; IL56306A0; AT377889B; SE7809290L; DK385578A; DK152480C; DE2809013A1; ATA704878A; JPS54118573A

Abstract

ABSTRACT OF DISCLOSURE

A circuit board having a conductor pattern fixed to one surface and having its opposite surface free of conductor patterns. Spaced perforations having metal walls extending through the circuit board and being connected to the conductor pattern at the one surface. At least one component mounted at the conductor pattern surface side of the circuit board and having component wires extending through the perforations and projection from the conductor pattern free surface of the board.
A solder joint filling the space between the component wire and the metal hole wall and extending upwardly in the perforations from the conductor pattern free surface of the board and being substantially flush with such surface. The method of forming such board by heating the projecting ends of the conductor wires in a hot, molten solder bath and causing the hot metal to flow upwardly on the wire into the perforation.

Description

83 11317~6 1 This invention relates to circuit boards and more par-ticularly to the connection and soldering of components to such boards a~d to the method and article produced thereby.
: Circuit boards for mounting and interconnecting elec-S trical and elec~ronic components have been produced and used for a long time. One type of such circuit boards is manufactured from a board of insulating material, for example, a board of molded phenolic or epoxy resin, to which is laminated on one side of the board a copper foil. To the copper foil laminated side of such board is applied a printed mask of m~terial resis-tant to copper etching reagents. The printed mask corresponds to the required conductive pattern. The CQpper in the areas left free by the printed mask is etched away and subsequently ~he printed mask layer is removed. The conductive copper pattern remaining when the mask layer is removed as well as the under-laying insulating material is provided with perforations for receiving the connector wires of the components at points in the pattern where soldering eyes or lands have been provided in said pattern. Subsequently, the components are mounted on the circuit boards by inserting the connector wires from the conductor-free ; side, through such perforations, and soldering the extruding leads to the respective conductors or conductor lands.
Another type of circuit board is manufactured by scribing and bonding pre-formed conductors, such as wires, along paths between pairs of terminal points or soldering eyes on an - insulating base, such as a moulded board of phenolic or epoxy resin. Perforations for receiving component connector wires are provided in such wire scribed board either before the wire is scribed thereon o, thereafter. Subsequent to wire scribing and .:
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~11 1 1~31746 1 perforation of the wire scribed board, the components are mounted thereon by inserting the connector wires through the perforations much in the same manner as in the printed circuit board.
In order ~o produce a soldered connection between the connector wires of the component and the soldering eye in the appropriate conductive path on the printed circuit and wire scribed circuit boards, it is necessary to carry out the mounting of the components in such a way that the connector wires are introduced into the respectively associated perforation holes ., 10 from the side of the board free of conductive paths. The con-: nector wires are then connected electrically and mechanically to the conductive paths or, respectively, their soldering eyes,e.g.,i : a bulk soldering process by bringing the side of the board bear-ing the conductive paths into contact with a tin solder bath, for example, by means of a drag-soldering bath device or a solder wave devlce.
'~ In such soldering process not only is the soldering eye coated with tin solder but also the whole of the pattern of ' conductive paths. This causes not only a functionally useless 20 excessive use of tin solder but often leads to the formation of solder bridges between adjacent conductive paths. The miniatu-rization of co~ponents has increased the densi~y of the conducti~ e paths and, hence, has reduced the distances between conductive paths and between conductor paths and the soldering eyes. With unprotected conductive paths, the danger of the formation of solder bridges and short-circuits is increased. To a~oid bridge~
and s rt-circuits it has become necessary to cover over the

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` 113~746 1 conductive paths for drag or wave soldering by imprinting a solder-resistant protective layer or mask over the conductor paths while leaving the soldering eyes or lands free of such soldering resistant mask. Soldering masks are applied either by screen printing or, in the case of so-called fine-conductor boards having greatly reduced distances between the conductive paths, by photographic printing. Such masks fulfill their purpose but lead to increasing of the price and complication of the production of the printed circuit boards and increase manu-facturing rejections.
A further disadvantage of the mounted printed circuitboards described above is the relatively frequent occurrence of unreliable so-called "cold" soldering points. Here a costly checking and finishing of the mounted printed circuit boards becomes necessary after the soldering process. It has been found that, in spite of careful testing, the occurrence of defective soldering points in later service cannot,with certainty be avoided. In addition, such printed circuit boards tend, during the mounting process, to become damaged at the soldering eyes.
It has, heretofore, been proposed to improve the qua-lity of the soldering points by utilizing printed circuit boards having a pattern of conductive paths applied to one side of the board and to provide the walls of the perforations for receiving the connector wires of the components with a metal coating con-nected electrically and mechanically to the respectively asso-ciated conductive paths. If one starts out from molded laminate, laminated on one side with copper or provided on one side with :
: ~, 1 scribed wire, the walls of the holes are, for example, in accord-ance with known methods, provided with a metal coating by means of currentless metallization, alone or in combination with galvanic deposition of metal. This considerably improves the soldering point quality because, in the soldering process, not only is a connection produced between the soldering eye and the connector wire from the component but, at the same time, the interstice between the connector wire and the metal coating on the wall of the hole is filled with the solder. Thus, the length of the electrical connection is increased and, at the same time, a mechanical connection is formed.
Circuit boards having metal coated perforation walls, however, have a considerably increased tendency to solder bridge formation. Thus, the application of a soldering mask, with its additional costs and disadvantages in method technique is neces-sary. The need for exact orientation of the applied soldering mask layer with the pattern of the conductive paths and holes imposes severe demands upon the process of applying the soldering mask. The soldering mask m~st be applied in registration with the conductor pattern to insure, on the one hand, that all of the soldering eyes and walls of the holes remain completely free of mask material while, on the other hand, all of the conductive paths are completely and reliably covered over. If this is not achieved, a worsening of the soldered connections occurs, leading to unusability, and/or conductor bridge formation.
In order to avoid this waste-charged and relatively costly process it has heretofore been proposed to completely coat B the pattern of conductive paths with a soldering mask layerf t~h , ` `` 1~31746 By so completely coating the pattern, the difficulty of the exact registration of the mask image with the pattern of the conductive paths is indeed avoided. However, because the mask is applied before the production of the perforations, a costly process of metallization of the walls of the holes is necessary in order to insure that the thickness of the mask layer is reliably bridged over and mechanically and electrically secure contact is produced with the conductive path associated in each case, with the metallization of the hole wall, which contact must also be fully preserved under temperature and mechanical loadings. To improve the behavior of the soldering and to compensate for the fact that connector wire of the component, because of the omission of a soldering eyP or land, is only connected to the end face of the conductive path forming part of the hole wall and the metalliæation of the hole walls, special metallization processes become necessary which, in the course of the metallization process, form substitute soldering eyes on the surface of the soldering mask layer. Apart from the fact that such a method and the associated baths are difficult to control, circuit boards of that kind can neither before nor after mounting be tested for their operational soundness in a way suited to practical operàtion.
With the rapid advance of small or miniaturized components and, hence, the necessity of higher conductor density on circuit boards, circuit boards which have conductive paths on both board sides and have perforations provided with a metal coating, have become more desirable. In such circuit boards, however, the board side coming into contact with the solder must sd~J -6-. .

~ 1131746 1 again be provided with a soldering mask in order to avoid the formation of solder bridges. Mounted circuit boards of ~hat kind exhibit an outstanding solder joint quali~y but are elaborate in production and, hence, costly.
The high density of conductive paths which can be accommodated on one side of a circuit board by wire scribing technique, or employing printed circuits fine line conductor technology does in many cases, for example, in the broadcasting and television equipment, allow the accommodation of all the conductor paths on only one side of the circuit board. However, such boards, provided on one side with a pattern of conductive paths or bare scribed wires and, by necessity, relatively small clearances between conductive paths and between conductor paths and soldering lands or joints when bulk-soldered, such as by drag or wave soldering, show a rather pronounced tendency to form solder bridges combined with inadequate soldering at the soldering points. The latter may, in known manner, be avoided by the employment of perforations or holes wi~h metallized walls, which, however, leads to a further increased tendency to solder bridge formation and, hence, make the application of solder masks practically unavoidable. Their production in the case of fine-conductor boards, having regard to accuracy of the registration on the one hand and the necessary resolution on the other, is costly and difficult and, for numerous fields of application, is excluded for economic grounds.
\ An object of the present invention is to provide a simple and economical circuit board having components mounted thereon and connected thereto in which the circuit board is free ~ 746 1 of the formation of solder bridges or other undesirable connec-tions, and having solder joints of excellent quality.
In the instant invention, circuit boards provided on one side with conductive paths of the conductive pattern and have perforations or holes with metallized walls for receiving the connector parts, for example, component leads, are employed.
The components are fitted to the side provided with the pattern of conductive paths and the component leads are connected, elec-trically and mechanically, by means of a soldering process per-formed from the side of the board free of conductor paths. Thesolder fills the interstice between the metallization of the wall of the hole and the component leads or pins and, preferably, reaches to the circuit board surface carrying the conductor paths to cover over or fill ~he region of the soldering land or eye or a corresponding restricted region of the conductive path.
Advantageously, the metalli~ation of the walls of the hole does not substantially reach beyond a circle approximating the hole diameter and/or the edge of the hole on the side of the board free of conductor paths. It is thereby ensured that, even in the case of conductor paths and the component holes asso-ciated with them being arranged extraordinarily closely, no short-circuits can occur by bent over ends of component leads with conductor paths or metal coatings reaching onto the surface.
The printed circuit board or wire scribed circuit board, in the practice of the instant invention, with the conduc-tor or circuit pattern on one side of the board and the other side of the board free of conductor or circuit patterns, is provided with perforations through the board at the ends or I-"~ 1131746 1 points in the conductor or circuit pattern at which component connections are to be made. Such perforations may be provided through the board before the circuit pattern is formed or scribed or may be formed, such as by drilling of the board, after the S conductors or circuit pattern has been completed. The walls of the perforations are next, either electrolessly or in combination with a galvanic plating process, coated with metal. Preferably, the metal coating of the perforation walls extends along the wall of component holes, up to the surface of the circuit board free of conductors or circuit patterns, without substantially e~tendin~
onto said surface, along such perforation wall to the side of the board bearing such conductors or circuit patterns and, preferably, reaches to the surface of the associated conductor to at least cover a region of the said conductor around the perfora-tion opening on the conductor or circuit pattern side.
Advantageously, the metallization of the walls of thehole does not reach beyond the edge of the hole on the side of th~
board not provided with conductive paths. It is thereby ensured that even in the case of conductive paths and the perforations associated with them being arranged extraordinarily closely, no short-circuits can occur by bent over ends of connector wires from the components with metal coatings reaching on to the surface With the conductor or circuit pattern on one side of the circuit board, the board perforated at the points where the components are to be connected and the walls of such perforations metal coated, the components are mounted on the circuit board from the side of the circuit board bearing the conductors or circuit pattern. This may be accomplished with automatic assem-31~46 1 bling equipment or by hand and is carried out by inserting the component leads, connector wires or pins through the component mounting holes where the connections are to be made.
The wire connector on the components utilized in the practice of the instant inven~ion are smaller, in diameter, than the inside diameter of the opening in the metal coated wall perforations and are longer than required to pass through the circuit board with the component in place. Thus, when the compo-nents are in place on the side of the circuit board bearing the conductor or circuit pattern, the component wires fit loosely in the perforation holes and project outwardly from the opposite side of the circuit board which side is free of circuit pattern conductors.
With the component wires extending loosely through the perforations and projecting from the circuit pattern free side of the board, the projecting ends of the component wires are lowered into a pan containing hot, mol~en solder. This is accomplished by positioning the circuit board, with the component~ ;
thereon, over the molten solder containing pan, with the conduc-tor and circuit pattern free side of the board facing the molten solder and then lowering the board toward the solder so that the projecting ends of the component wires are immersed in the hot, molten solder and the circuit pattern free board surface touches the solder surface.
The hot, molten solder heats the ends of the component wires and, as this is being accomplished, the molten solder is drawn upward, along the component wires and between such wires and the metal coated walls of the perforation holes, by capillary 11 ~ i 7 ~

1 action. Thus, the space between the metal coated perforation wall and the component wire or lead at each of the component con-nections is filled with solder which forms a mechanical and an electrical connection between such wire and such metal coated hole. The molten solder flows upward through the perforation hole and, to a certain degree, outward at the top of the hole over a pad-area of the respec~ive conductor around the perfora-tion opening at the component side of the circuit board.
~fter the molten solder has been drawn upward into ~he space between the component wires or leads and the metal coated hole walls and has filled such space, the ends of the conductor wires are lifted out of the molten solder by lifting the board and the solder cools and solidifies forming a permanent mechani-cal and electrical connection between the component wires or leads or pins and the circuit board.
The instant invention will be more fully understood from the following description and Examples of preferred embodi-ments taken with the appended drawings in which ~ igure 1 is a perspective view, partly in section, showing a printed circuit board to which components are to be applied in accordance with the instant invention;
Figure 2 is a perspective view similar to Figure 1 but showing another embodiment of the conductor pattern;
Figure 3 is an enlarged side view, in section, showing a portion of the circuit board, a metal coated circuit board perforation, a component and a component wire, lead or connector in such perforation above the hot, molten solder bath before the immersion of the component wire end in the molten bath per the process of the instant invention;

` 1131746 Figure 4 is an enlarged view, similar to Figure 3 but showing the e~d of the component wire immersed and the process of the invention underway;
Figure 5 is an enlarged side view, in section, showing the component mounted thereon in accordance with the instant invention.
Figure 6 shows a perspective partial illustration of a printed circuit board having a plurality of different electrical and/or electronic components mounted.
lo Re~erring now to the drawings, printed circuit board, generally designated 1, of a suitable carrier material, is pro-vided only on one side, namely, on the mounted side 8, with conductor paths 2 in a predetermined conductor pattern. The con-nection or mounting points of the conductor pattern are charac-terized by mounting holes 9 which are through-metallized or coated with a metal layer 3. The side 7 of the printed circuit board 1 opposite the conductor path pattern is provided with no kind of electrically-conductive tracks at all and the ~etal layer 3 of the walls of the holes ends here is substantially flush with the surface 7 without the formation of any sort of collar. Con-ductor paths 2 may be formed by the printing circuit process and the perforations 9 may then be metallized or conductor paths 2 m~y be scribed wires followed by metallizing of the walls of perforations 9.
Referring to Figure 3, component lead 5 of an electri-cal or electronic component 6 is mounted on circuit board 1 so that the end of wire S stands out freely at the side 7 of the printed circuit board 1 which side 7 is free of conductor paths.
As best shown in Figures 4 and 5, when the end of wire S is immersed in hot molten solder 4, molten solder 4 flows up around wire 5 ~ith perforation 9 between wire 5 and metal wall 3 and, ` 1131746 l at 4a, fills the interstice between the metal wall 3 of the perforation and the connector wire 5 as well as the region of the soldering eye on the mounting side 8, Figure 5. Thus, the soldering process is performed from the side 7, in which case the freely projecting end of the connector wire 5 is acted upon by heat and the solder rises from the bottom upwards in the ..
interstice by a kind of capillary action, fills up the hole in this way in the manner illustrated, but project beyond the region having the metal collar~ Thus, solder 4a is nearly flush with the end of metal wall 3 at the side 7 and projects beyond metal wall 3, over the metal collar at.mounting side 8. Excess tin solder remains exclusively on the freely projecting end of the component lead 5 and does not overlap the cross-sectional area of the perforation on the side from which the soldering process is effected. On the opposite circuit board side 8, carrying conductor paths 2, the maximum solder cover is substantially over only the metal collar round the wall of the hole because the solder is drawn upwards from the underlying side 7 and flows onto the mounting side 8 radially from inside to outside. The surface tension of the solder prevents solder 4a from flowing over the edge of the collar or land areas at circuit board side 8.
Figure 6 shows a perspective partial illustration of a printed circuit board having a plurality of different electrical ~ and/or electronic components mounted... It is essential here too ; 25 that a start is made from a circuit board l which bears conduc-tor paths 2 only on one side, and that on the side 8 bearing the conductor paths 2, all of the components 6 lie while the side 7 is k t free o~ conductor patbs and components. The surface 7 is . -13-` 1131746 1 merely characterized in that the free ends of the connector wires 5 from the components 6 project from it more or less in order to guarantee ~he heat contact necessary in the soldering process.
The side 7 of the board, not bearing the conductor paths of the conductor path pattern or components, is advanta-geously provided with printed information, for example, with characterizing and test data useful to the mounting and operation .
an image of the conductor path pattern and the like. In this case, it is of particular advantage that side 7 of the board, apart from the mounting holes, is-completely free and available for printing of this kind.
The production of the mounted printed circuit boards provided with components and in accordance with the invention is to be described below by way of example.
EX~MPLE 1 In a preferred embodiment, a base material, for example , a phenolic paper press laminate is used, one side of which is provided with an adhesion-promoting layer. After the production of the perforations intended as mounting holès for component leads, the board is prepared in known manner for electroless metal deposition and sensitized catalytically, for exa~ple, with a solution of a tin-palladium-chloride-complex and exposed to a metallization bath working without e~ternal current supply, to provide the adhesion-promoting layers, as well as the walls of the holes, with a thin, preferably 1 to 6 microns thick metal layer, preferably a ductile copper layer. Deposits of metal which may be present on, and loosely adhering to the side of the board not provided with the adhesion-promoting layer are removed by brushing or other suitable way.

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1 Then the negative of the required pattern of conductor paths is applied, in mask form, by means of screen or photographi .
printing or some other method in order subsequently to build up the conductor paths simultaneously with the metallization of the walls of the holes by galvanic deposition of metal to the desired thickness. To this end, a copper layer of preferably 2~ to 40 microns is deposited. Instead of galvanic deposition of metal, the build up of the conductor paths, as well as the metallization of the walls of the holes, may be achieved in the same way by 1~ means of electroless deposition of metal, preferably depositing a ductile copper layer of appropriate thickness.
The masking layer is next removed and ~he thus exposed thin electrolessly deposited metal layer between the conductor paths is removed in known manner. This is achieved, for example, in a simple form by the action of an etching agent for a period of time adequate for removing the thin metal layer without residue and without, at the same time, reducing the thickness of the conductor paths to a substantial degree.
The board, finished in a known manner by blanking and other manufacturing processes, is then provided with the compo-ments mounted from the side of the board bearing the conductor paths of the conductor pattern, e.g., by means of automatic com-ponent lead insertion machinery, or by hand, so that the wires from the components reach at least slightly beyond the plane of the edges of the holes on the side of the board free of conductor paths. The board thus prepared is preferably subjected to a bulk soldering process, for example, a drag soldering device.
The end of the connector wires from the components, reaching into the bath of hot, solder metal, bring about contact 1` 1131746 1 with the hot solder at sufficient depth to satisfactorily heat the wire, so that the solder rises up between the component wire and the metal coating of the wall of the holes, fills the inter-stice between the two and preferably forms a coating of solder on the associated surface of the conductor path on the opposite side of the board in regions of small extent similar to soldering pads or lands. The soldered connections thus produced are of extraordinary reliability. The outlay upon inspection and check-ing of solder joints and respectively touch-up of imperfect solde .
joints is superfluous or at least largely reduced and at the same time the quantities of rejects are drastically reduced. The high mechanical strength of the soldered connections thus achieve brings about great reliability in service of the mounted printed circuit boards in accordance with the invention even under unfavorable service conditions such, for example, as under vibration.
According to a preferred embodiment of the method according to Example 1, boards provided with printed mask are subjected, in pairs, to the galvanic or electroless deposition of metal for the build up of the conductor paths and the metalliza-tion of the walls of the holes. With the sides of the boards which are not to be provided with conductor paths brought into the metallizing bath solution facing one another.

As the starting material,a base material is used which - as well as the adhesion-promoting layer is applied to one side - contains a substance which is catalytic to the electroless deposition of metal so that in the case of process of Example 1 , ```` 1131746 1 the step of catalyzation is unnecessary. Thus, a further simpli-fication of the production process is achieved.

As the starting material, a solid epoxy resin board blank is employed having applied to one side an adhesion-promotin layer containing a substance which acts catalytically upon the electroless deposition of metal applied. Af~er providing ~he board blank with the holes of the component mounting hole pattern a negative pattern mask of the conductor paths is applied, for example, by the method of photographic printing. After appro-priate treatment of the adhesion-promoting layer in an oxidizing medium for the production of a microporous surface, the board is brought into a bath for electrolessly depositing ductile copper and left there for a period of time adequate to building up the conductor paths and metallize the walls of the holes to the desired thickness. Depending upon the choice of the mask mate-rial, after completion of the metal deposition the mask layer is either removed or preferably, however, left on the board, The back is then provided with the required printed information.
Subsequently, the components are mounted on the board from the side bearing the conductor paths and, the soldered connections between component leads and conductor circuitry are formed in accordance with the instant invention employing one of the known bulk soldering methods with the conductor-free board side facing the solder pot.

A molded epoxy resin laminated paper board provided on one side with copper foil, is first provided with the pattern of component mounting holes. The board is exposed to a tin-~ 11317~6 l palladium-chloride-complex solution, thus being catalyzed for electroless deposition of copper and a thin copper layer is subsequently formed by electroless deposition. Then the surface is provided with a galvanic plating bath resistant masking layer for~ing a negative of the required conductive pattern. A copper layer of the desired thickness is then deposited in the areas not covered by said masking layer including the hole walls and the masking layer subsequently removed.Finally, the thus exposed thin copper film between the conductor paths is removed, e.g., by spray etching. After known final fabrication steps, the printed circuit board is provided with the components by insertin the component leads from the side bearing the conductor paths of the conductor pattern, with said lead wires projecting at least slightly beyond the edges of the holes on the opposite side of the board free of conductor paths. Subsequently, as previously described, the soldered connections are produced by dip or drag soldering from the side free of conductor paths and ~omponents and in accordance with the invention.
In the practice of the instant invention, even in the case of very narrow clearances between conductor paths, soldering masks are not required. At the same time, high quality of solder joints is achieved simply and economically.
The mounted printed circuit boards in accordance with the instant invention are distinguished by low reject rates and high reliability in service. Through the metal layer on the walls of the holes, together with the arrangement of the compo-nents on the side bearing the conductor paths, great electrical and mechanical reliability of the soldered connection is achieved --, 3l746 1 The absence of conductor paths on the soldering side of the board prevents the formation of solder bridges as well as the danger of short-circuit formation by bent-over component lead wires in a reliable and inexpensive manner. The large area available for printed information allows to provide detailed measuring and operating data and instructions as well as components specifica-tions employed and the pattern of the conductor paths.
The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the feature shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

Claims

WHAT IS CLAIMED:

1. A circuit board provided with components mounted on it, said board comprising on one of its surfaces a pattern of conductors and having its opposite surface free of any such conductor pattern, a plurality of perforations extending through said board at spaced points along said conductor pattern at which points connections to component leads are made, a metal coating on the wall of said perforations, at least one component mounted on the surface of said board provided with the conductor pattern, said component having at least one component lead ex-tending through one of said perforations extending through said board and projecting outwardly beyond the conductor free circuit board surface and a solder connection between said component con-nection wire and said metal coating on the wall of said perfora-tion, said solder connection being substantially flush with the conductor free surface of said circuit board.

2. The circuit board, as claimed in claim 1, in which said solder connection substantially flush with the conductor free surface of said circuit board extends into said perforation between said component connection wire and said metal coating and forms an electrical and mechanical connection therebetween.

3. The circuit board, as claimed in claim 1, in which said solder connection extends through said perforation between said component connection wire and said metal coating and extends outwardly at the conductor and component side of said circuit board and forms a solder pad on the conductor around said perforation at said conductor side.

4. The circuit board, as claimed in claims 1, 2 or 3, in which said circuit board is a printed circuit board.

5. The circuit board, as claimed in claims 1, 2, or 3, in which said circuit board is a wire scribed circuit board.

6. A method for mounting and connecting components to a circuit board having a conductor pattern on one surface and an opposite surface free of conductor patterns and provided with perforations having metal coated walls extending from the conduc-tor pattern on said one surface through the circuit board to said opposite surface free of conductor patterns comprising the steps of inserting the lead wires of the components to be connected to said circuit board through said perforations from the side of said circuit board having said conductor pattern surface so that the ends of said lead wires project from said circuit board from the side of said board having said conductor pattern free surface and immersing the projecting end of said component lead wires in a bath of hot, molten solder to heat said lead wires and cause said hot, molten solder to flow upwardly, into said perforation, between said heated lead wire and said metal coating and, after said solder has so flowed upwardly, removing said lead wire ends from said hot, molten solder bath and cooling and solidifying said solder between said metal coating and said lead wire, thus forming the respective solder joints.

7. The method, as claimed in claim 6, in which said projecting component lead wire ends are maintained in said hot, molten solder bath until the volume between said metal coated per-foration wall and said lead wire is completely filled.

8. The method, as claimed in claim 6, in which said projecting component lead wire ends are maintained in said hot, molten solder bath until the volume between said metal coated perforation wall and said lead wire is filled and said solder forms a solder pad around said perforation at the respective conductor surface on conductive pattern and component side of said circuit board.