GB1600550A

GB1600550A - Method of and apparatus for inserting terminal pins in a substrate

Info

Publication number: GB1600550A
Application number: GB1223778A
Authority: GB
Original assignee: Pye Electronic Products Ltd
Current assignee: Pye Electronic Products Ltd
Priority date: 1978-03-29
Filing date: 1978-03-29
Publication date: 1981-10-21

Description

(54) METHOD OF AND APPARATUS FOR INSERTING TERMINAL PINS IN A SUBSTRATE (71) We, PYE (ELECTRONIC PRODUCTS) LIMITED, of St. Andrew's Road, Cambridge CB4 1 DP, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed,to be particularly described in and by the following statement: The invention relates to a method of and apparatus for the insertion of one or more terminal pins in a substrate. The stbstrate may be, for example, a printed circuit board.

Electrical and electronic equipment is increasingly being designed on a modular basis in which a plurality of modules are plugged into a larger printed circuit board, normally referred to as a "mother board". As equipment is miniaturised both the modules and the mother board become smaller and thus the tolerances of the plugs and sockets used become more critical. Further, since one reason for a modular construction is to ease the problem of maintenance by enabling a repair by the substitution of a new module in place of a faulty module, the tolerance must be held for module production over many years.

A known connection system used in mobile radio receivers depends on accurately drilling a printed circuit board which forms part of the module and inserting terminal pins into the accurately drilled holes. The end of each of the terminal pins is then riveted to hold it firmly on the printed circuit board. This is an expensive assembly technique since the degree of accuracy required demands high precision and is difficult to achieve. Dimensional variations of the board are produced, for example, by temperature changes or moisture absorption. Inaccuracies may also arise because of variations of the drilling machine with time and temperature. Also when drilling several printed circuit boards simultaneously the drill tends to wander as it goes through several thicknesses.

It is an object of the invention to provide a method of assembling therminal pins into a substrate in which the precision of the location of the terminal pins is not dependent on the precision of the location of the holes receiving them.

The invention provides a method of locating one or more terminal pins in a substrate, comprising the steps of forming a corresponding number of oversized holes in the substrate, one for each of the desired terminal-pin locations; locating the terminal pins in an insertion head designed to hold each pin in a desired position and orientation; producing relative meovement between the insertion head and substrate so that a portion of each terminal pin penetrates a respective one of the holes; causing solder to flow around the portions of the terminal pins within the holes while the pins are held in the insertion head; allowing the solder to solidify and hold the pins in position; and releasing the pins from the insertion head.

It may be advantageous, particularly when the terminal pins are gold-plated, to tin at least the portions of the terminal pins which penetrate the holes in the substrate before the relative movement is effected. If the terminal pins are gold-plated the gold may migrate into the solder in the holes and give it a coarse grainy appearance. Pre-tinning of at least the portions which penetrate the holes reduces this effect.

The invention further provides a method of locating one or more terminal pins in a substrate, comprising the steps of forming a corresponding number of oversized holes in the substrate, one for each of the desired terminalpin locations, filling the or each hole with solder; locating the terminal pins in an insertion head designed to hold each pin in a desired position and orientation; heating the terminal pins to a temperature sufficient to melt the solder in the holes; producing relative movement between the insertion head and substrate so that the heated terminal pins press against and penetrate the solder in the holes and cause the solder to flow around the portions of the pins are held in the insertion head; allowing the terminal pins to cool so that the solder solidifies and holds the pins to cool so that the solder solidifies and holds the pins in position; and releasing the pins from the insertion head.

The portions of the terminal pins which penetrate the holes in the substrate may be tinned before the relative movement is effected.

The insertion head may comprise a block having holes to locate the terminal pins, being heated by conduction of heat from the block.

The terminal pins may be held in the block by a partial vacuum and may be released from the block by removing the partial vacuum and replacing it with a compressed-air supply. A heat shield may be located between the block and the substrate.

The invention still further provides appara tus, when in use, for locating one or more terminal pins in a substrate, the apparatus com prising an insertion head for locating each ter minal pin in a desired position and orientation; means for holding each terminal pin in the in sertion head; means for positioning a substrate having solder-filled oversized holes in a desired position relative to the insertion head; means for heating the terminal pins to a temperature sufficient to melt the solder; means for effect ing relative movement between the insertion head and substrate so that portions of the ter minal pins located in the insertion head press against and penetrate the solder in the holes in the substrate and cause the solder to flow around said portions of the pins; and means for releasing each terminal pin from the inser tion head after the solder has solidified.

The insertion head may comprise a block having holes for the location of terminal pins.

The holes may communicate with a chamber formed within the block or between the block and a further member. Means may be provided for reducing the air pressure within the chamber to below atmospheric pressure and for in creasing the air pressure within the chamber to above atmospheric pressure. The block or the further member may be heated by means of an electrical heater.

Means may be provided for tinning at least the portions of the terminal pins which pene trate the holes in the substrate.

The means for positioning the substrate may be provided with a recess or aperture to accom modate components assemble don the substrate.

The apparatus may comprise a heat sheild for positioning between the block and the sub strate, the heat shield being provided with apertures through which the terminal pins project.

In order that the invention may be more readily understood an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, of which: Figure 1 shows a printed circuit board pro vided with holes to enable terminal pins to be .inserted by a method according to the invention, Figure 2 is a cross-sectional view on line AA of Figure 1 of the area adjacent to one of the holes, Figure 3 shows apparatus according to the invention for inserting terminal pins into a sub strate, Figure 4 is an underneath view of the pin insertion head of the apparatus shown in Figure 3, Figure 5 is a cross-sectional view on line BB of Figure 4, Figure 6 shows in schematic form a control arrangement for the apparatus shown in Figure 3, Figure 7 shows a pin-positioning device for use with the apparatus shown in Figure 3, and Figure 8 shows a heat shield for use with the apparatus shown in Figure 3.

Figure 1 shows a printed circuit board 1 having a plurality of holes, one of which is shown at 2. Figure 2 is a cross-sectional view of Figure 1 on line AA and shows a terminal pin 3 inserted in the hole 2. The terminal pin 3 comprises a shank portion 4 which is designed to mate with a socket, a shoulder portion 5 which lies against the surface of the printed circuit board 1 and a root portion 6 which extends into the hole 2 in the printed circuit baord. The root portion 6 has a smaller diameter than that of the hole 2 in which it is inserted. Typical dimensions are as follows: hole 2 - 1.1 mm diameter shank portion 4 - lmm diameter x 2.5 mm long shoulder portion 5 - 2 mm diameter x 1.2 mm long root portion 6 - 0.8 mm diameter x 0.8 mm long thickness of printed circuit board 1 - 0.8 mm A method of locating one or more terminal pins in a printed circuit board according to the invention comprises the steps of providing a printed circuit board having holes 2, one for each of the desired terminal-pin locations, of larger diameter than the portions 6 of the terminal pins to be inserted in the holes; locating the terminal pins in an insertion head designed to hold each pin in a desired position and orientation; producing relative movement between the insertion head and substrate so that a portion of each terminal pin penetrates a respective one of the holes; causing solder to flow around the portions of the terminal pins within the holes; allowing the solder to solidify and hold the pins in position; and releasing the pins from the insertion head.

The holes 2 may be filled with solder while the pins are held in position by the insertion head. In order to achieve this it is necessary to provide access to the side of the printed circuit board opposite to that against which the shoulder portion 5 is positioned. It may be possible to fill the holes 2 with solder when using a single-sided printed circuit board without through-plated holes but a better anchorage of the terminal pins is achieved if the hole is through-plated. Double-sided printed circuit boards normally have their holes through-plated to provide electrical connection between the conductive tracks on opposite sides of the board.

In order to provide a good electrical contact and resistance to corrosion the shank portion 4 of the terminal pin, which is the portion which mates with a socket in equipment into which the printed circuit board is plugged, may be gold-plated. As the pins are relatively small, e.g. 1 mm x 4 mm, it is convenient to gold-plate the whole pin and not merely the shank portion 4. However, the gold on the root portion 6 tends to migrate into the solder within the hole during the soldering operation. To avoid this the root portion 6 of the pins may be tinned before the soldering operation is effected. It is convenient to perform the tinning operation while the pins are held in the insertion head.

A further method of locating electrical terminal pins in a printed circuit board according to the invention comprises the steps of providing a printed circuit board having holes 2, one for each of the desired terminal-pin locations, of larger diameter than the portions 6 of the terminal pins to be inserted in the holes; filling each hole with solder; locating the terminal pins in an insertion head designed to hold each pin in a desired position and orientation; heating the terminal pins to a temperature sufficient to melt the solder in the holes; producing relative movement between the insertion head and substrate so that the heated terminal pins press against and penetrate the solder in the holes, and cause the solder to flow around them; allowing the terminal pins to cool so that the solder solidifies and holds the pins in position; and releasing the pins from the insertion head.

The holes 2 may be filled with solder by wave soldering after the circuit components have been assembled onto the board. In this way a separate manufacturing operation to fill the holes 2 with solder is not required. It may be possible to fill the holes 2 with solder when using a single-sided printed circuit board without through-plated holes but a better anchorage of the terminal pins is achieved if the hole is through-plated. Double-sided printed circuit boards normally have their holes throughprinted to provide electrical connection between the conductive tracks on opposite sides of the board.

In order to provide a good electrical contact and resistance to corrosion the shank portion 4 of each terminal pin, which is the portion which mates with a socket in equipment into which the printed circuit board is plugged, may be gold-plated. As the pins are relatively small, e.g. 1 mm x 4mm, it is convenient to gold-plate the whole pin and not merely the shank portion 4. However, the gold on the root portion 6 tends to migrate into the solder within the hole during the insertion procedure. To avoid this the root portions 6 of the pins may be tinned before the relative movement is effected. It is convenient to perform the tinning operation while the pins are held in the insertion head.

The insertion head may be a plate, mesh or block having accurately located holes or recesses for holding the terminal pins. In one form the insertion head comprises a metallic block having accurately machined holes in which the terminal pins are placed and held by means of a partial vacuum. The block accommodates electrical cartridge heaters which heat the terminal pins by the conduction of heat from the block. The block is lowered onto the printed circuit board so that the root portions 6 of the terminal pins press against the solder in the holes 2 and melts the solder so that it flows round the pins. The pins are then allowed to cool and when the solder has solidified are released from the block by removing the partial vacuum. As an aid to releasing the terminal pins and to force-cool the terminal pins, air may be blown from the back of the block through the holes therein.

If the pins are inserted after assembling electrical components on the board and performing a wave soldering operation then it may be desirable to insert a heat shield between the insertion head and the printed circuit board.

When using a heated metal block as the insertion head the heat radiated by the block may be sufficient to damage components on the printed circuit board if no precautions are taken A heat shield in the form of a titanium plate having holes through which the terminal pins pass may be arranged between the insertion head and the printed circuit board.

The printed circuit board may be pre-heated before the terminal pins are pressed agianst the solder in the holes in the printed circuit board.

This will enable the rate of rise of temperature of the components on the board to be more readily controlled and hence reduce risk of damage to the components. Also the insertion time for the terminal pins will be reduced due to the temperature of the solder in the holes being nearer to the melting point of the solder.

The method according to the invention has been described with reference to the insertion of terminal pins in printed circuit boards but it could be used for the insertion of terminal pins in other substrates, e.g. thick-film circuits.

Apparatus according to the invention for inserting terminal pins in a printed circuit board is shown in Figures 3 to 6. The apparatus comprises a base plate 30 having locating means 31 for a printed circuit board, and an insertion head 32 which is arranged to be lowered towards the base plate 30 by means of a handle 33. The insertion head 32 comprises a metal block 320 which is heatd by three cartridge heaters 321. Attached to the metal block 320 is a member 322 having a number of holes 323 arranged to receive the shank portions 4 of the terminalpins. The member 322 is attached to the block 320 by four screws 234 andis designed for use with printed circuit boards having given terminal-pin locations. The member 322 will be replaced by a similar member having different locations for the holes 232 when terminal pins are required to be inserted in different locations in other printed circuit boards.

A chamber 325 is formed between the metal block 320 and member 322, from which cham ber an air pipe 326 leads. The air pipe is coupled to a compressor/vacuum pump (shown schematically in Figure 6) which is arranged to increase or reduce the air pressure in the chamber 325.

The locating means 31 comprises a series of recesses 311 which are arranged to accommodate the components mounted on the printed circuit boards, and two locating pegs 312. The printed circuit boards may be arranged on strips, each strip carrying a number of printed circuit boards along its length, the printed circuit boards being separated only after all operations on them have been completed. The strips are provided with holes into which the locating pegs 312 fit to align the printed circuit board with the insertion head 32. If the printed circuit boards are not arranged on a strip, holes to mate with the locating pegs 312 would be provided in the printed circuit board itself.

The head 32 is raised and lowered by means of handle 33 which is pivoted on a bracket 34 attached to a top plate 35. The top plate 35 is supported above the base plate 30 by two pillars 36 and 37 which pass through clearance holtes 38 and 39 in the insertion head 32. A rod 40 is attached to the insertion head 32 and pivotally attached to the handle 33 to transmit the movement of the handle 33 to the insertion head 32, the rod passing through a clearance hole 41 in the top plate 35.

The electrical feed to the heaters 321 is from a control unit 60 via path 61. A temperaturesensing device arranged to sense the temperature of the metal block 320, for example a thermocouple, is connected to the control unit via a path 62. The control unit 60, which may be, for example, the temperature controller sold by Pye Ether Limited as the "MINI" Series 1990B temperature controller, is settable to a desired temperature and will control the supply of power to the heaters 321 to keep the temperature of the insertion head 32 at the desired value. Two limit switches 63 and 64 are provided to control a valve unit 65 which connects the chamber 325 to either a source 66 of less than atmospheric pressure or a source 67 of greater than atmospheric pressure.

In the operation of the above apparatus terminal pins are loaded into the holes 323 in the insertion head 32 and held in position by a partial vacuum. The handle 33 is held down and the insertion head operates limit switch 63, .which is fixed relative to the top plate 35, to cause the valve unit to connect source 66 to the chamber 325. The printed circuit board is located on the pegs 312 and the insertion head loweverd to press the terminal pins against the solder in the holes in the printed circuit board.

At the lower limit of travel of the insertion head 32 limit switch 64, which is mounted in a fixed position relative to the bottom plate 30, is operated and causes the valve unit 65 to couple the source 67 to the chamber 325. The source 67 may be, for example, a compressedair line normally found in manufacturing facilities. This air will, on entering the chamber 325, force the pins out of the holes 323 and cool them at the same time so that the solder solidifies around the pins and firmly locates them within the holes. The insertion head 32 is then raised and the printed circuit board removed.

Figures 7 and 8 show accessories for use with the apparatus shown in Figures 3 to 6. Figure 7 shows a jig 70 which comprises a metal block 71 having a pattern of holes 72 formed therein to receive the root portions 6 of the terminal pins. The jig is provided with a handle 73 and two holes on its underside which are arranged to mate with the locating pegs 312.

The jig is used to load terminal pins into the insertion head 32. The root portion 6 of a terminal pin is located in each hole 72 in the jig.

The jig is then located under the insertion head 32 on the locating pegs 312. The insertion head 32 is then lowered until the shank portions 4 of the terminal pins project into the holes 323 in the insertion head. The thickness of the jig 70 is arranged so that the insertion head 32 cannot be lowered far enough to operate limit switch 64 when the jig is positioned beneath it. Hence the terminal pins are held in the holes 323 in the insertion head by a partial vacuum when the insertion head is raised.

Figure 8 shows a heat shield 80 for use with the apparatus shown in Figures 3 to 7. The heat shield 80 comprises a titanium plate provided with holes 81. The heat shield 80 is arranged to lie between the insertion head 32 and the printed circuit board. In use terminal pins are located in the holes in the jig 70 and the heat shield 80 located on the jig so that the shank portions 4 of the terminal pins project through the holes 81 in the heat shield. The terminal pins are then held in the holes 323 of the insertion head 32 as described hereinbefore.

The shoulder portion 5 of the terminal pins 5 hold the heat shield 80 against the insertion head 32. The insertion head is then lowered to press the root portions 6 of the terminal pins against the solder in the holes in the printed circuit board. The insertion head is then raised when the solder has flowed round the pins and the heat shield 80 is removed from the terminal pins after the solder has solidified.

The apparatus described requires considerable skill and dexterity from the operator. The quality of the finished result will depend on the following factors: 1) the heating time of the pins in the insertion head; 2) the force with which the pins are pressed against the solder in the holes in the printed circuit board; 3) the time allowed for the solder to flow around the pins; 4) the speed and smoothness of withdrawal of the insertion head from the pins; 5) the time allowed for the solder to solidify before removing the heat shield from the printed circuit board and removing the printed circuit board from the apparatus; and 6) the care taken in loading and unloading the printed circuit board into and from the apparatus.

It is necessary, therefore, if consistent results are required, to ensure that the operator of the apparatus has the necessary skill and training.

It has been found that with the apparatus described satisfactory results may be achieved when the block temperature is between 250"C and 450"C, typically 300"C, with the following values for the factors 1) to 5).

1) The heating time of the pins in the insertion head is between 2 and 6 seconds, typically 3 seconds.

2) The force of the pins against the solder in the holes in the printed circuit board is up to 4 lbs, typically 2 lbs.

3) The time allowed for the solder to flow round the pins is between 1 and 10 seconds, typically 6 seconds.

4) The speed of withdrawal of the insertion head from the pins is between 0.5 and 2 inches per second, typically 1 inch per second.

5) The time allowed for the solder to solidify before removing the heat shield is between 0.5 and 4 seconds, typically 1 second.

In order to reduce the dependence on the skill and care of the operator, apparatus in which some of the functions 1) to 6) are mechanised has been proposed.

The apparatus may comprise a fixed insertion head, a loading slide into which the terminal pins would be inserted, a solder pot, and a further slide on which the printed circuit boards are loaded. The insertion head would be heated to a controlled temperature and be supplied with a vacuum/compressed air supply. The loading slide would be equivalent to the jig 70 and be provided with holes to locate the root portions of the terminal pins. The heat shield would then be located over the pins and the slide located under the insertion head where they would be held by suction. The slide would then be lowered and removed from under the insertion head and be available for loading with the next set of terminal pins. The solder pot would then be positioned under the insertion head and raised so that the root portions of the terminal pins are dipped into the pot, which would then be rotated to tin the root portions of the terminal pins. The solder pot would then be lowered and removed.

The further slide would then be indexed so that a printed circuit board is located under the insertion head and the slide raised so that the solder in the solder-filled holes in the printed circuit board is pressed against the root portions of the terminal pins. After penetration of the solder by the terminal pins and a dwell time to allow the solder to flow and then solidify, the slide would then be lowered and the heat shield removed. The loading of the terminal pins and the printed circuit boards on the slides could, therefore, be carried out remotely from the insertion head and be carried out while pins are being inserted in a previously loaded printed circuit board. The movement of the slides and the solder pot could be controlled automatically, movement of the slides being detected to cause a vacuum or compressed air to be supplied to the insertion head at the appropriate time.

WHAT WE CLAIM IS: 1. A method of locating one or more terminal pins in a substrate, comprising the steps of forming a corresponding number of oversized holes in the substrate, one for each of the desired terminal-pin locations; locating the terminal pins in an insertion head designed to hold each pinin a desired position and orientation; producing relative movement between the insertion head and substrate so that a portion of each terminal pin penetrates a respective one of the holes; causing solder to flow around the portions of the terminal pins within the holes while the pins are held in the insertion head; allowing the solder to solidify and hold the pins in position; and releasing the pins from the insertion head.

2. A method according to Claim 1, in which at least the portions of the terminal pins which penetrate the holes in the substrate are tinned before the solder is caused to flow around the portions of the terminal pins within the holes.

3. A method according to Claim 1 or 2, in which the insertion head comprises a block having holes to locate the terminal pins.

4. A method as claimed in Claim 3, in which the terminal pins are held in the block by a partial vacuum.

5. A method as claimed in Claim 3 or 4, in which the terminal pins'are released from the block by removing the partial vacuum and substituting a compressed-air supply.

6. A method of locating one or more terminal pins in a substrate, comprising the steps of forming a corresponding number of oversized holes in the substrate, one for each of the desired terminal-pin locations, filling the or each hole with solder; locating the terminal pins in an insertion head designed to hold each pin in a desired position and orientation; heating the terminal pins to a temperature sufficient to melt the solder in the holes; producing relative movement between the insertion head and substrate so that the heated terminal pins press against the penetrate the solder in the holes and cause the solder to flow around the portions of the pins within the holes while the pins are held in the insertion head; allowing the terminal pins to cool so that the solder solidifies and holds the pins in position; and releasing the pins from the insertion head.

7. A method according to Claim 6, in which at least the portions of the terminal pins which penetrate the holes in the substrate are tinned before the relative movement is effected.

8. A method according to Claim 6 or 7, in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. before removing the heat shield from the printed circuit board and removing the printed circuit board from the apparatus; and 6) the care taken in loading and unloading the printed circuit board into and from the apparatus. It is necessary, therefore, if consistent results are required, to ensure that the operator of the apparatus has the necessary skill and training. It has been found that with the apparatus described satisfactory results may be achieved when the block temperature is between 250"C and 450"C, typically 300"C, with the following values for the factors 1) to 5).

8. A method according to Claim 6 or 7, in

which the insertion head comprises a block having holes to locate the terminal pins, the terminal pins being heated by conduction of heat from the block.

9. A method as claimed in Claim 8, in which the terminal pins are held in the block by a partial vacuum.

10. A method as claimed in Claim 8 or 9, in which the terminal pins are released from the block by removing the partial vacuum and replacing it with a compressed-air supply.

11. A method according to Claim 8, 9 or 10, in which a heat shield is located between the block and the substrate.

12. A method according to any of Claims 6 to 11, in which the substrate is preheated before the terminal pins are pressed against the solder in the holes in the substrate.

13. A method as claimed in any preceding Claim in which the substrate is a printed circuit board.

14. A method of locating one or more terminal pins in a substrate substantially as described herein with reference to Figures 1 and 2 or Figures 1 to 6,7 or 8 of the accompanying drawings.

15. Apparatus, when in use, for locating one or more terminal pins in a substrate, comprising an insertion head for locating each terminal pin in a desired position and orientation; means for holding each terminal pin in the insertion head; means for positioning a substrate having solder-filled oversized holes in a desired position relative to the insertion head; means for heating the terminal pins to a temperature sufficient to melt the solder; means for effecting relative movement between the insertion head and substrate so that portions of the terminal pins located in the insertion head press against and penetrate the solder in the holes in the substrate and cause the solder to flow around said portions of the pins; and means for releasing each terminal pin from the insertion head after the solder has solidified.

16. Apparatus as claimed in Claim 15, in which the insertion head comprises a block having holes for the location of terminal pins.

17. Apparatus as claimed in Claim 16, in which the holes communicate with a chamber formed within the block or between the block and a further member.

18. Apparatus as claimed in Claim 17, including means for reducing the air pressure within the chamber to below atmospheric pressure.

19. Apparaus as claimed in Claim 17, including means for increasing the air pressure within the chamber to above atmospheric pressure.

20. Apparatus as claimed in Claims 16 to 19, in which the block or the further member is heated by means of an electrical heater.

21. Apparatus as claimed in any of Claims 15 to 20, comprising means for tinning at least the portions of the terminal pins which penetrate the solder in the holes intf;e substrate.

22. Apparatus as claimed in any of Claims 15 to 21, in which the means for positioning the substrate is provided with a recess of aperture to accommodate components assembled on the substrate.

23. Apparatus as claimed in any of Claims 16 to 22, comprising a heat shield for positioning between the block and the substrate, the heat shield being provided with apertures through which the terminal pins project.

24. Apparatus for locating electrical terminal pins in a substrate substantially as described herein with reference to Figure 3 to 6, 7 or 8 of the accompanying drawings.

25. A substrate having one or more terminal pins located thereon by the method claimed in any of Claims 1 to 14.