AUTOREGULATING MULTI CONTACT HEATER

Abstract: Contacts of a multipin connector may be soldered to leads of a board of the like by forming coatings of magnetic materials on each contact and locating the contacts between poles defined by an air gap of the magnetic core, each pole having a separate pair of opposed pole pieces disposed adjacent a pair of contacts whereby upon application of a constant a.c. current to a coil would about the core the magnetic material is heated to a temperature approaching its Curie temperature whereby temperature regulation occurs.

Description: The present invention relates to the soldering of complex structures such as multipin electrical connectors by means of autoregulating Curie point heating. The application of autoregulating Curie point heaters, such as disclosed in U.S. Patent No. 4,256,945, to the soldering of multipin surface mounted connectors has proved to be a difficult task. Where single contact connectors are encountered, a heater such as a soldering iron may be employed. The soldering of multiple contact connections on non-complex shapes has been proposed in EPA-02066l9. However, attempts at soldering complex-shaped surface mounted devices employing inductive coupling to a Curie point heater have encountered flux leakage problems which have rendered these approaches inefficient, resulting in excessive Joule heating and potential damage to adjacent delicate electronic components. According to the present invention, there is provided an arrangement for soldering a multipin connector to a support that bears a plurality of conductors, comprising a multipin connector having a plurality of contacts spaced along it, each multipin connector contact including a ferromagnetic material having a Curie temperature above the melting point of a fusible material employed to solder the contact to a conductor on said support, and electromagnetic energiser means for inducing an alternating electric current in each multipin connector contact to generate Joule heat sufficient to raise the ferromagnetic material to its effective Curie temperature thereby to achieve autoregulating heating to melt the fusible material, said energiser means including a core of a high electrical impedance, high permeability material with opposed poles defining an air gap and having an alternating current energising coil to establish magnetic flux across the gap, each pole having a plurality of spaced pole pieces each paired with a respective one of the opposed pole pieces on the other pole with the spacing along the air gap between successive pairs of opposed pole pieces corresponding to the spacings of the multipin connector contacts along the multipin connector and the widths across the gap between the opposed pole pieces of the pairs of poles being such that the presence of the multipin connector contacts in the gap in alignment with respective pairs of opposed pole pieces substantially completes the flux paths between the opposed pole pieces. The invention further provides a method for soldering contacts of a multipin connector to electrical conductors on a support, comprising providing on each multipin connector contact a ferromagnetic material with an effective Curie temperature above the melting point of a fusible material employed to solder each contact to a conductor on said support, positioning the multipin connector on the support, placing the contacts of the multipin connector, while in position on the support, within the air gap between poles on a core of an electromagnetic energiser having an a.c. energising coil, and energising the coil thereby to induce an a.c. current in each contact sufficient to raise the ferromagnetic material to its effective Curie temperature and achieve autoregulating heating to melt the fusible material, the poles of the core being configured to provide a row of spaced pole pieces on one pole and a corresponding row of opposed pole pieces on the other pole with the spacings, in the direction along the rows, between successive pairs of opposed pole pieces matching the spacings of the contacts along the connector and the air gap width between the two pole pieces of each opposed pair being selected such that the presence of the contacts in the air gap in alignment with the pole pieces substantially completes the flux paths between the opposed pole pieces. Preferably, the core of the energiser has a conductivity less than 10⁻⁸ ohm-cms. In the preferred embodiment, a coil wound core of high resistance, low loss magnetic material has multiple, shaped pole pieces to concentrate flux in ferromagnetic material forming part of each contact pin of a multipin connector whereby each pin is efficiently heated to a temperature approaching its Curie temperature at which temperature autoregulation becomes effective. The core material may be powdered iron or a ferrite having resistivities as high as 10⁹ ohm-cms and having low hysteresis losses. Ferrites cover a wide range of Curie temperatures; 120°C. - 500°C. and permeabilities; 20-5000. Powdered iron cores have very high Curie temperatures. By using such materials the eddy current and hysteresis losses and thus core losses are quite low. The arrangement permits the high flux density of the core to be transferred to the ferromagnetic material of the contacts further increasing efficiency and thus good autoregulation. The core may take the general form of a rectangle having one side interrupted to provide opposed poles. The poles are then intended to be disposed on opposite sides of a multipin connector the contacts of which have a ferromagnetic covering whereby each contact pin becomes a self-regulating heater. The core may thus be shaped to closely accommodate a connector in its air gap, the connector having an array of spaced contacts or contact groups and the poles of the core having an opposed pair of shaped pole pieces for each contact or contact group of the array whereby each pole piece pair concentrates flux into its respective juxtaposed contact or contact group. Curved, straight, wavy and irregular contact arrays can be accommodated by providing similarly configured rows of corresponding pole pieces. Arrangements in accordance with the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a top view of a multipin connector; Figure 2 is a side view of a multipin connector; Figure 3 is a side view of a core with a multipin connector in its air gap; Figure 4 is a top view of a core with a multipin connector in its air gap; and Figures 5A, 5B and 5C illustrate different configurations of pole piece arrays on the core. Referring now to Figures 1 and 2 of the accompanying drawings, there is illustrated a multipin connector 2 to be secured to a circuit board or the like. The connector comprises a plurality of upstanding pins 4 and 6 arranged in pairs and secured in a base 8 of the insulating material. The pins 4 and 6 terminate below the base 8 in outwardly extending conductive legs 10 and 12, respectively having feet 14 and 16 intended to contact, for instance, a printed circuit board 18. As can be seen in the example of the multipin connector of Figure 1, a connector may have two rows of pins of indefinite numbers each, eight being illustrated in two rows of four each. The legs 10 and 12 have coverings 20 and 22 respectively, on all surfaces except the contact surface, of ferromagnetic material which has an effective Curie temperature sufficient to melt solder or the like. The connector is to have each foot soldered to a different printed circuit lead or in some instances two or more to the same lead. As an example, the left feet of Figure 1 are all secured to a lead 24, the upper two feet on the right side are to be connected to a lead 26 and the lower two right side feet are to be connected to separate leads 28 and 30. Referring now to Figures 3 and 4, there is provided a heater energiser circuit comprising a high impedance generally rectangular core 31 having a gap 32 lying between poles 34 and 36 of the core. The core has a winding 38 disposed about a side 40 opposite gap 32. The core is elongated perpendicular to the plane of the core, i.e. the plane of the page as illustrated in Figure 3. Each pole is provided with a row of triangular slots or recesses to define a row of shaped pole pieces 42 on one side of the gap and a row of pole pieces 44 on the other side of the gap. Each of the pole pieces 42 is aligned with a respective pole piece 44 on the other side of the gap so that a direct flux path is established between each pair of opposed pole pieces. When in use, the core 31 is positioned with each pair of opposed pole pieces having located therebetween opposed feet 14 and 16 of a pair of the pins 4 and 6 of the multipin connector 2 of Figures 1 and 2. The magnetic materials 20 and 22 covering the legs of the pins complete the magnetic path across the gap whereby a path of low reluctance is established. Upon energisation of coil 38 with a constant alternating current, the magnetic materials 20 and 22 are heated to a temperature approaching their Curie temperatures. When the temperature has risen sufficiently, the materials 20 and 22 become paramagnetic and since the current is constant and the available current now spreads into the low resistance material of the legs 10 and 12, which is copper for instance, the heating is marginally reduced, the temperature of the member falls, and the members 20 and 22 become magnetic again, so that the cycle is repeated and autoregulation results. The pole pieces 42 and 44 are shaped so as to concentrate flux in the magnetic layers 20 and 22 and are located very close to and in some instances in contact with the layers 20 and 22 to minimise the magnetic reluctance of the path. Also in multipin connectors of the type under consideration the gap between the legs 10 and 12 is quite small further contributing to a low reluctance magnetic path. The array of pole pieces does not have to be a straight row and the pole pieces do not have to be rectangular in cross section. A curved or even wavy or irregular array of pole pieces is permitted all as illustrated in Figures 5A, 5B and 5C. Also the pole pieces can be cylindrical to avoid sharp corners that induce leakage flux. It should be noted that the current supplied relative to the minimum cross-sectional area of the magnetic path should be such that saturation does not occur along the magnetic path. Saturation, it must be realised, greatly increases leakage flux and contributes to inefficient operation and in the presence of sensitive components can destroy a chip or the like. The material of the core is preferably a powdered iron or a ferrite. One appropriate ferrite is available from Fair Rite Products as Product No. 861103001. This material is a ferric oxide mixed with other oxides, has a mu of approximately 125 and a conductivity of approximately 10⁻⁹ ohm-cms. The term "constant current" as employed herein does not mean a current that cannot increase, but means a current that obeys the following formula where I is the load current. Specifically, in order to autoregulate, the power delivered to the load when the heater exceeds Curie temperature, must be less than the power delivered to the load below Curie temperature. If the current is held invariable, then the best autoregulating ratio is achieved, short of controlling the power supply to reduce current. So long, however, as the current is controlled in accordance with the above formula, autoregulation is achieved. Thus, when large self regulating ratios are not required, constraints on the degree of current control may be relaxed thus reducing the cost of the power supply. The above equation is derived by analysing the equation: P = [I²R] where P is power and I is the current in the load. Differentiating with respect to R dP dR = |I|² + 2R|I| dI dR to satisfy the requirements for self regulation dP/dR>O. Thus, which reduces to the above equation. It should be noted, however, that the more constant the current the better the self regulation.

Claims: An arrangement for soldering a multipin connector (2) to a support (18) that bears a plurality of conductors, comprising a multipin connector (22) having a plurality of contacts (10,12) spaced along it, each multipin connector contact including a ferromagnetic material (20,22) having a Curie temperature above the melting point of a fusible material employed to solder the contact to a conductor on said support, and electromagnetic energiser means for inducing an alternating electric current in each multipin connector contact to generate Joule heat sufficient to raise the ferromagnetic material to its effective Curie temperature thereby to achieve autoregulating heating to melt the fusible material, said energiser means including a core (31) of a high electrical impedance, high permeability material with opposed poles (34,36) defining an air gap (32) and having an alternating current energising coil (38) to establish magnetic flux across the gap, each pole having a plurality of spaced pole pieces (42) each paired with a respective one of the opposed pole pieces (44) on the other pole with the spacing along the air gap (32) between successive pairs of opposed pole pieces (42,44) corresponding to the spacings of the multipin connector contacts (10,12) along the multipin connector (2) and the widths across the gap (32) between the opposed pole pieces (42,44) of the pair of poles (34,36) being such that the presence of the multipin connector contacts (10,12) in the gap (32) in alignment with respective pairs of opposed pole pieces (42,44) substantially completes the flux paths between the opposed pole pieces (42,44). An arrangement according to Claim 1, wherein said core (31) is of a ferrite material. An arrangement according to Claim 1 or Claim 2, wherein said core (31) is of a low hysteresis loss material and has a conductivity of less than 10⁻⁸ ohm-cms. An arrangement according to any preceding claim, wherein said coil (38) is connected to a constant current a.c. source. An arrangement according to any preceding claim, wherein the pole pieces (42,44) on each pole (34,36) are arranged in a straight row. An arrangement according to any one of Claims 1 to 4, wherein the pole pieces on each pole are arranged in a row of curved or wavy or irregular configuration. A method for soldering contacts of a multipin connector (2) to electrical conductors (24,26,28,30) on a support (18), comprising providing on each multipin connector contact (10,12) a ferromagnetic material (20,22) with an effective Curie temperature above the melting point of a fusible material employed to solder each contact (10,12) to a conductor (24,26,28,30) on said support (18), positioning the multipin connector (2) on the support (18), placing the contacts (10,12) of the multipin connector, while in position on the support (18), within the air gap (32) between poles (34,36) on a core (31) of an electromagnetic energiser having an a.c. energising coil (38), and energising the coil thereby to induce an a.c. current in each contact (10,12) sufficient to raise the ferromagnetic material (20,22) to its effective Curie temperature and achieve autoregulating heating to melt the fusible material, the poles (34,36) of the core (31) being configured to provide a row of spaced pole pieces (42) on one pole (34) and a corresponding row of opposed pole pieces (44) on the other pole (36) with the spacings, in the direction along the rows, between successive pairs of opposed pole pieces (42,44) matching the spacings of the contacts (10,12) along the connector (22) and the air gap width between the two pole pieces (42,44) of each opposed pair being selected such that the presence of the contacts (10,12) in the air gap (32) in alignment with the pole pieces (42,44) substantially completes the flux paths between the opposed pole pieces.

Inventors: DOLJACK, FRANK A. 3181 CANDON COURT
Applicants: METCAL INC.
Application year: 1988
Main classification: B23K3
IPC codes: H05K3, B23K1, H01F3, H01R43, B23K3