Throughput of a two-sided printed board and method for producing it

Abstract: The object of the description is a flexible throughput of a two-sided printed board (1), by which ruptures and electric breaks caused by the different thermal expansion properties of the materials in known throughputs are avoided, and which nevertheless allows the use of an inexpensive printed board material and of the wave soldering method. According to the invention, two holes are made into the printed board, into one of which a metal sleeve (4) is inserted. The sleeve is sur­ rounded by a conductor foil (2), i.e. soldering fringe on the upper surface of the printed board. The second hole (5) is without a sleeve and comprises a conductor foil, i.e. solde­ ring fringe on the lower surface of the printed board. The overshoot wire (6) is composed on the printed board so that its one arm (6a) is placed into the sleeve (4) and its other arm (6b) extends through the hole (5) below the printed board. In wave soldering, the lower surface of the printed board (1) touches the molten solder, which rises from the sleeve (4) and fixes this by soldering to the overshoot wire (6) and the up­ per foil (2) and simultaneously the second arm (6b) of the wire (6) is soldered to the lower conductor foil (3).

Description: The present invention relates to the throughput of a two-sided printed board, in which the upper conductor foil of the printed board is connected directly or by means of a component with the lower conductor foil, the upper joint having been produced by a sleeve inserted into a hole in the printed board in such a manner that molten solder has risen through the sleeve from below the printed board and has fixed the top of the sleeve to the upper conductor foil. It is known from FR-A-2 184 437 to form the throughput simply so as to place into the hole in the printed board, at the point of which a conductor foil is provided on each side, a metal sleeve, through which the molten solder rises by capillary force, thus soldering both the upper and the lower conductor foil to the sleeve. Although such a joint is extremely easy to produce, one of its drawbacks is that the solder joint might break because of the stiffness of the joint and of the different thermal expansion coefficients of the printed board and the sleeve material, particularly if the printed board is subject to temperature variations. When the temperature variations continue, the rupture grows and may eventually lead to an electric break. This problem can be somewhat reduced by using a printed board material having more advantageous thermal expansion characteristics (e.g. glass fibre material FR-4), but such a material is more expensive as well as harder to work. DE-A-3 521 752 discloses a throughput of a two-sided printed board, in which the upper conductor foil is connected directly or by means of a component with the lower conductor foil, the upper joint having been produced in such a manner that molten solder has fixed one arm of the wire, inserted into a hole of the printed board, to the upper foil, and the other arm has been inserted through a second hole, which ends at the lower foil, said arm being fixed to the lower foil by soldering. DE-A-1 065 898 is related to a method for manufacturing conductive connections between conductor foils of printed board being provided on different sides of an isolating plate by means of soldering. Soldering is provided on that side of the isolating plate being opposite to the soldering device between the conductor strip and the connector element. The soldering melts by means of the heat conducting through the connector element and connecting the connector element with the conductor strip. It is also known to use wires connecting the upper and the lower foil in order to produce more flexible joints, but the known embodiments do not allow a rapid production by means of the wave soldering method. The purpose of the present invention is to eliminate the above problems and to provide a joint and a method that ensure operation reliability in spite of temperature variations, and allowing simultaneously the use of an inexpensive printed board material and the application of the wave soldering method. In order to achieve this purpose, the throughput according to the invention is characterized by the features presented in claim 1, and the characteristics of the method according to the invention are correspondingly disclosed in claim 2. In the throughput method according to the invention, two holes are consequently required in the printed board. Into one of the holes, a sleeve is inserted in a manner known per se, and it comprises a solder fringe on the upper surface of the printed board, surrounding the sleeve. Around the other hole, whore no sleeve is provided, a solder fringe, i.e. conductor foil is disposed on the lower surface of the printed board. The second hole and the one with the sleeve are connected by means of an overshoot wire or some other component, the molten solder rising in a wave solder joint by capillary attraction along the sleeve onto the upper surface of the printed board, thus forming an upper solder fringe, and the second solder joint is produced at the second hole onto the lower surface of the board. Thus, a flexible and reliable joint is achieved between the lower and the upper surface of the printed board. The over-shoot wire or component acts as a flexible element, which compensates the different thermal expansion properties of the various materials taking part in the joint; the printed board, the sleeve, the overshoot wire and the solder. Under these circumstances, the solder joints, when subject to temperature variations, are not subject to stresses that would cause ruptures and electric breaks. The invention and its other features and advantages are described in greater detail below and with reference to the enclosed drawing, which is a perspective and partial section view of the joint achieved according to the invention. In the figure, reference 1 indicates a printed board, which can be for instance of FR-2 material and which comprises upper conductor foils 2 and lower conductor foils 3. A joint produced by means of an overshoot wire is described below. In the printed board 1 two holes have been made, into one of which a metal sleeve 4 has been inserted and the other hole 5 is without a sleeve. In the sleeve 4 a planar upper flange 4a is provided, which is placed against the conductor foil 2. The lower side of the sleeve is also spread out of a flange 4b, at which no conductor foil is provided, however. The metal overshoot wire 6 has been composed into the printed board in such a way that its one arm 6a extends through the sleeve 4 and the other arm 6b extends through the hole 5. In the case of automatic soldering, as the solder wave sweeps the lower surface of the board, the molten solder rises along the sleeve 4 by capillary attraction, thus soldering the flange 4a to the upper foil 2 at the point 7 and simultaneously the arm 6a to the sleeve 4. At the same time the molten solder fixes the arm 6b to the lower foil 3 at the point 8. In wave soldering, a flexible joint is thus achieved between the upper foil 2 and the lower foil 3. Corresponding totally to the overshoot wire 6, the throughput can of course be produced by means of the component 9, as shown in the centre of the figure. The one arm or foot 9a of the component is attached by the solder 7 risen along the sleeve to the upper foil and the second arm, i.e. foot 9b, is attached by the solder 8 to the lower foil 3. By using two sleeves 4 the component 9 can, by means of the method described above, automatically be soldered inbetween the two upper conductor foils as shown on the right side in the figure.

Claims: Throughput of a two-sided printed board (1), in which the upper conductor foil (2) of the printed board is connected directly or by means of a component with the lower conductor foil (3), the upper joint (7) having been produced by a sleeve (4) inserted into a hole in the printed board (1) in such a manner that molten solder has risen through the sleeve from below the printed board (1) and has fixed the top (4a) of the sleeve to the upper conductor foil (2), and one leg (6a; 9a) of a wire (6) or the component (9) has been inserted into the sleeve (4), said leg being joined to the sleeve (4) by soldering, and a second leg (6b; 9b) of the wire (6) or component (9) has been inserted through a second hole (5) in the printed board, the second hole ending at the lower conductor foil (3), and said second leg (6b; 9b) being fixed to the lower conductor foil (3) by soldering (8), whereby no conductor foil is provided on the printed board around the lower part of the sleeve (4) nor around the top part of the second hole (5). Method for producing the throughput of a two-sided printed board (1), in which the upper conductor foil (2) is connected directly or by means of a component to the lower conductor foil (3), the upper joint (7) being produced by inserting a sleeve (4) into a hole in the printed board (1) in such a manner that molten solder rises through the sleeve from below the printed board (1) and fixes the top (4a) of the sleeve to the upper conductor foil (2), and one leg (6a; 9a) of a wire (6) or a component (9) is placed into the sleeve (4), said leg being fixed to the sleeve (4) by the rising solder, a second leg (6b; 9b) of the wire (6) or component (9) is inserted through a second hole (5) in the printed board (1), said second hole ending at the lower conductor foil (3), the solder (8) fixing said second leg (6b; 9b) to the lower conductor foil (3), whereby the printed board (1) is left free from conductor foil around the lower part of the sleeve (4) and around the top part of the second hole (5).

Inventors: ANTTIO MARKKU ILMARI, SUOMINEN AARRE TAPANI, ANTTIO, MARKKU ILMARI, SUOMINEN, AARRE TAPANI
Applicants: SALORA OY
Application year: 1989
Main classification: H05K3
IPC codes: H05K3