CA1258755A - Soldering device, flux and method - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides a solder joint compris-ing at least two elongate substrates connected together by a mass of solder having associated therewith a substantially colourless solder flux and a temperature indicating component and enclosed within a heat-recovered substantially transparent polymeric mem-ber, the temperature indicating component having changed from a coloured state to a substantially colourless state to enable the connection to be visually inspected.

Description

87S~j Thls Inventlon re/ates to a heat-recoverab/e solderIng dev/ce, to methods of solderlng uslng such a dev/ce, to tempera-ture Indlcatlng so/der flux composltlons and to the use of such composltlons In so/derlng.

Thls applIcatlon Is a dlvlslonal applIcatlon of copend-lng appllcatlon No. 412,782 flled October 4, 1982.

Heat-recoverab/e so/derlng dev/ces are known In the 10 art. See, for example, U.S. Patents Nos. 3,316,125 to Sherlock, 3,305,625 to Ellls, 3,316,343 to Sherlock, 3,396,460 to Wetmore and 3,396,894 to Ellls. Such heat-recoverable devlces generally comprlse a heat-shrln~able polymerlc sleeve havlng a fuslble Insert comprlslng solder. Elongate substrates, such as a palr of 1~ w/res, are /nserted /nto the s/eeve and heat /s applled causlng the s/eeve to shrlnk /nto contact wlth the substrates. The heat also causes the solder to melt and flow around the substrates.
Upon coo/ Ing, a solld solder Jolnt Is formed between the sUb-strates. In general, the temperature requlred to me/t the solder 20 Is hlgher,than the temperature requlred to shrlnk the sleeve.
Thus, vlsual observatlon that the sleeve has completely recovered does not necessarlly mean that the temperature necessary for sol-derlng has been reached. There /s, therefore, no vlslble Indlca-tlon durlng the solderlng process that enough heat has been applled. Further, In the event that a soldered Jolnt so formed falls durlng use, there Is no way of subsequently Inspectlng the Jolnt to determlne whether the fallure was due to Inadequate heatlng durlng the solderlng process.

Copendlng appllcatlon No. 412,782 descrlbes and clalms a solderlng dev/ce comprlslng a substantlally transparent heat-recoverable polymerlc member a fuslble so/der Insert posltloned wlthln sa/d member and a so/der flux composltlon whlch /s assocl-ated wlth sald solder Insert and whlch undergoes a vlslble co/our change at a crltlcal temperature.

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The polymerlc member Is substantlally transparent to the extent that the vlslble colour change of the solder flux can be seen through the member. Thls devlce thus advantageouslY pro-vldes a clear vlslble Indlcatlon that a solder Jolnt or connec-tlon has reached the correct solderlng temperature, The copendlng appllcatlon a/so dlscloses and clalms a method of solderlng at /east two solderable substrates whlch com-prlses posltlonlng sald substrates wlthln a heat-recoverable 10 solderlng devlce accordlng to the f/rst aspect of the present Inventlon, and heatlng sald dev/ce, thereby causlng sald heat-recoverab/e member to recover Into contact wlth sald substrates and sald flux to undergo a vlslble colour change. Preferably the devlce Is arranged such that the heatlng step causes the heat-recoverable member to recover Into contact wlth the substratesbefore the flux undergoes a vlslble colour change. Preferably the substrates are generally elongate.

Copendlng appllcatlon No. flled on even date herewlth dlscloses and clalms a solder flux composltlon whlch compr/ses solder flux and a react/ve component, the flux compos/-tlon undergolng a chemlcal react/on resultlng In a vlslble co/our change at a crltlcal temperature.

Thls Inventlon a/so provIdes a method of solderlng at /east two solderable substrates /ocated adJacent each other, whlch compr/ses applylng to sald substrates a quantlty of solder and a flux composltlon accordlng to sald thlrd aspect of the pre-sent Inventlon, and applylng heat to sald substrates, solder and flux composltlon untll a vlslble co/our change In sald flux com-posltlon occurs.

Accordlng to the present Inventlon there Is provlded a solder Jolnt comprlslng at least two elongate substrates con-nected together by a mass of solder havlng assoc/ated therewlth asubstantlally co/our/ess solder flux and a temperature Indlcatlng .

- 2 -~25~3755 component and enc/osed wlthIn ~ heat-recovered substantlally transparent polymerlc member, the temperature Indlcatlny compo~
nent havIng changed from a co/oured state to a substantlallY
co/our/ess state to enable the connect/on to be vlsually Inspected.

The heat-recoverab/e member of the dev/ce of the pre-sent Inventlon Is capable of vndergolng a change In Its dlmen-slonal conflguratlon on appllcatlon of heat. Thls change /n dlmenslonal conflguratlon /s usually toward an orlglnal shape from whlch It has prevlously been deformed, but the term "heat-recoverab/e~J as used hereln, a/so Includes a member whlch, on heatlng, adopts a new conflguratlon, even If It has not been pre-vlously deformed.

The heat-recoverab/e member of the devlce accordlng to sald flrst aspect of the present Inventlon generally compr/ses a heat-shrlnkable sleeve made from a polymerlc materlal exhlbltlng the property of elastlc or plastlc memory as descrlbed, for exam-ple, In U.S. Patents Nos. 2,027,962, 3,086,242 and 3,957,372.
The orlglnal dlmenslonally heat-stable form may be a translent form In a contlnuous process In whlch, for example, an extruded tube /s expanded, whl/e hot, to a dlmenslonally heat-unstable form but, In other methods of preparatlon, a preformed dlmenslon-ally heat-stable artlcle Is deformed to a dlmenslonally heat-unstable form In a separate stage.

In the productlon of the heat-recoverab/e member, the polymerlc materlal Is generally cross-llnked. One manner of pro-duclng a heat-recoverab/e artlcle compr/ses shaplng the polymerlc materlal Into the descrlbed heat-stable form, subsequently cross-llnklng the polymerlc materlal~ heatlng the artlcle to a tempera-ture above the crystalllne meltlng polnt, or for amorphous mate-rlals the softenlng polnt, of the po/ymer, deformlng the artlcle and coollng the artlcle whlle In the deformed state so that the 37~5 , -4- ~P0783 deformed state of the article is retained. In use, applica ~ , tion of heat will cause the article to dimensionally recover from the deformed state to the original heat-stable shape.

In other articles, as described, for e~ample, in U.S. Patent No. 4,207,364, an elastomeric member such as an outer tubular member is held in a stretched state by a second member, such as an inner tubular member, which, upon heating weakens and thus allows the elastomeric member to recover.

Examples of polymers used in the rnanu~acture of heat-recoverable articles include polyolefins, e g.
polyethylene and copolymers of ethylene with ethylenically ~` unsaturated monomers, such as ethylene/ethyl acrylate, .~ ` ethylene/vinyl acetate copolymers, polyvinyl chloride, elastomers, silicones, polytetrafluoroethylene, polyvinyl-idene fluoride, polyurethanes, and ionomers. The polymer can be cross-linked either by radiation or chemical means~

The heat-recovery temperature of crystalline polymers is generally a temperature slightly above the crystalline melting temperature. Polymers, such as polyvinyl chloride, which are not crystalline recover at about their glass transition temperature.

The wall thickness of the member is preEerably in the range of from about 0.0005 inch ~0.0127mm) to about 0.05 inch (1.2700mm) and is especially preferably from about 0.0008 inch (0~0203mm) to about 0.01 inch(0.2540mm)~

The solder insert may be positioned witllin the heat-recoverable member by coating solder onto the surface of the recoverable member. Alternatively, a solder preform of the desired configuration may be produced and this then ~2~;~75s inserted into the heat-recoverable mernber. The solder is positioned such that wllen two solderabié substrates are positioned within the device and the device is heated, the solder is forced into intimate con~act with the substrates by the recovery of the heat-recoverable member. ~hen the heat-recoverable member is in the form of a heat-shrinkable sleeve, the solder is preferably in the shape of a ring on the inner surface of the sleeve.

The flux aids the flow of the solder or cleans the surfaces of the substrates to be joined or both. Various solder flux compositons are known and are cornmercially available. Widely used as solder fluxes are compositions based on natural rosin. Other fluxes include, for example, . inorganic and organic acids. In use, the solder flux melts, 15 flows and covers the substrate surface at a temperature below the melting point of the solder. Thus the particular flux used will depend of the natuLe of the solder in a given `: application. ~ny solder flux can be used in accordance wit~
this invention. The ~lux comprises a temperature indicatinc component and the particular flux and the appropriate temperature indicating component to be used in a particular application can be readily ascertained by one skilled in th~
art without undue experimentation. The temperature indicatir . component is preferably one that is compatible with the flu~
and does not interfere with the normal functioning of the flux.
The solder flux is associated with the solder of the heat-recoverable soldering device. Any of the conven-tional means for associating flux with solder can be used.
For example, a solder preform can be coated with flux by spraying, dipping, brushing or the like, usually before it has been positioned within the heat-recoverable device.
The solder flux can also be used in soldering operations such as hand soldering, in which a heat-recoverable device is not employed. In this event, the flux can be coated on .: ' '` , ~ Z~87~S

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-6- MP07~3 the solder or can be positioned within the solder, for example, in the form of a core which can be in various configurations as is well known in the ark. The 1ux must be visible during the soldering process to detect the colour change in the flux when it reaches the appropriate temperature. It has been found that if the flux is positioned as a core within the solder, flow of the flux on heating renders it visible. A visible colour change occurs when the soldering temperature has been reached. In general, the soldering temperature is higher than the recovery temperature Thus continued heating is required after recovery in order to effect the visible colour change of the solder flux.

In accordance with this invention, the solder jflux composition contains a temperature indicator such j15 that the flux undergoes a colour change when heated to the appropriate soldering temperature. The colour change is preferably an irreversible colour change, that is a colour change that does not reverse, for example, when the solder and fl~x cool and solidify. Such an irreversible change 20 provides a continuing indication and permanent means or determining whether the soldered joint was heated to the required temperature during soldering. Thus improperly formed terminations can be detected by visual inspection after the sbldered connection is completed and cooled.

The colour change of the flux is preferably from a coloured state to a substantially colourless one. The completed solder joint is thus visible ~or inspection through the flux. In this way, the joint itsel can be inspected to check Eor ade~ate soldering and to detect improperly or-ned terrninations, as well as to check for application of sufficient heat during the soldering process by the change in colour of the fl~x.

The flux composition changes colour at a critical .

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- ~Z5i~755 ternperature. The desired critical temperature varies depending on the particuiar solder used The critical temperature is that temperature which is required to effect a solder connection with the particular solder, that is the temperature required to cause the solder to melt, ~low and wet the substrates so that on cooling the solder rnakes a mechanical and electrical bond between the substrates being soldered. The particular solder to be used varies depending on the substrates being joined and the material of the heat-recoverable member. The temperature re~uired to effect the solder terrnination is generally above the temperatu:
required to cause recovery of the heat-recoverable mernber.

Since the critical temperature varies with the ; nature of the solder, the temperature indicating component of the flux composition varies depending on the solder i used. Preferably, the flux composition undergoes a colour change in the temperature range of ~rom about 150C to about ` I 450C, especially preferably from about 200C to about 240C. The temperature of the colour change is preerably in the range of from about 20C to about 60~C above the melting point ~f the solder. Preferably, it is about 20C
to about 30C above the melting point of a low temperature solder and about 30C to about 60C above the melting point of a high temperature solder.

As stated above, the flux composition contains a temperature indicator such that at a critical temperature the flux composition undergoes a colour change. Various temperature indicators can be used, for example, azo dyes such as Pigment Red 73 (an azo dye prepared ~rom 2-nitro-p-30 toluidine and 2-naphthol, CI 12120), acid-base indicators such as Thymol blue, diazo dyes such as Acid Red 73 (a diazo dye derived from p-phenylazoaniline and 2-naphthol-6,8-disulfonic acid, CI 27290), and the like. In general, any dye which is compatible with the flux and which undergoes a colour change at a critical ternperature can be used.

` ~L2S~755 -8- ~P0783 Preferabl~ the ~lux composition contains a temp-erature indicator that is a chemically reactive component which undergoes a chemical reaction with the solder fluY~ at a critical temperature to produce a colour change~ Particularl preferred are flux compositions in which, at a critical temperature, the reactive component causes the flux composition to become colourless since this allows the soldered joint to be readily inspected. Suitable chemically reactive components are, for example, Bromocresol Green, Basic Fuchsine or Thymol Blue.

The temperature indicator may be incorporated into a solder flux composition by ~nown techniques. The amount of temperature indicator incorporated into the flux is ; preferably in the range of from about 0.01 to about 5 parts - ~ 15 per 100 parts of flux and is especially preferably from about O.O~ to about 2 parts per 100 parts of flux. The amount added depends on the intensity of the colour.
Sufficient temperature indicator should be added to provide a flux composition which is clearly visible during the soldering operation. The flux composition may also contain additives, for example, dispersing ~aids such as water, alcollol or a subfactant or emulsifier, buffers, such as an acid or salt to maintain the desired pH, for example, oxalic ` ` acid, lactic acid, maleic acid, tartaric acid, fumaric acid or citric acid, and stabilizers.

An embodiment of a device in accordance with the present invention will now be described by way of example, with reference to the accompanying drawings, wherein:

Figure 1 is a side view of a heat-recoverable device according to the present invention having two elongate substrates positioned therein;
Figure 2 is a side view of the device of Figure 1 after a solder joint has been effected between the elongate substrates.

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-9- MP~783 ln Figure 1, a heat-recoverable device cornprises a heat-recoverable member in thé ~orin of a tubular sléeve 3 - having a solder insert 4. The sleeve 3 is a heat-shrinkable tube of radiation cross-linked ethylene-tetrafl~oroeth~lene copolymer containing fusible thermoplastic inserts 5 toward each end of the tube. Prior to being positioned within the sleeve 3 the solder insert 4 is coated with a temperature indicating flux. The coated flux is dark blue in colour and thus obscures the grey colour of the solder insert.
, The unrecovered sleeve 3 is positioned over a coaxial cable 1 having a portion of the outer insulation removed to expose the underlying shield. The end region of a ground wire 2 with the insulation being removed froTn the end region lies adjacent the exposed shield of the ~5 cable 1. The sleeve 3 is ~hen heated causing it to shrink ;~.i;.~into contact with the cable and ground wire an~ to cause the solder to melt and flow. On heating, the flux changes colour at a temperature above the melting point of the solder becoming colourless. Heating is discontinued at this point. During heating of the sleeve, the thermoplastic inserts 5 melt and seal the sleeve to the cable. The resulting product is shown in Figure 2.

;In Figure 2, sleeve 3 has shrunk into contact with and is sealed to the cable 1. As the flux is now colourless, the grey colour of the solder, 4, is visib~e through the sleeve. The solder has thus affected a termination between the shield of 1 and the exposed tip of ground wire, 2~

The following Examples illustrate various solder flux compos~tions in accordance with the present invention.

~ EXA~PLES 1-14 Temperature indicating solder flux compositions .. ~ .
.
, ~L2S~3755 -10- MP07~3 were prepared by disperslng vario~s dyes in a Milros ~1611, a commercially available rosin-based flux comprising 37 of a mixture of rosin isomers in 63~ isopropyl alcohol.
The dyes used and the concentrations of dye in the result-ing temperature indicating E1UX compositions are listed in Table 1. Additives, as listed in Table 1, ~ere added as ~`. appropriate to aid in dissolution of the pigment or to buffer the solution to maintain the desired pH. The dyes used are:
Acid Red 73 (commercially available as Scarlet M
Crude), a diazo dye derived from p-phenylazoaniline and 2-naphthol-6,8-disulphonic acid. (Colour Index, : CI, 27290).

~i Pigment Red 3 (commercially available as Atlasol "``1 15 Spirit Red-3) an azo dye prepared from 2-nitro-p-"``~`1 ` toluidine and 2-naphthol. (CI 12120).

Thymol Blue, commercially available and also referred to as thymolsulphonphthalien.

Pigment Red 52 tcommercially availa~le as Garnet Toner ~2), an azo dye derived from 2-amino-5-chloro-p-toluenesulphonic acid and 3-hydroxy-2-naphthoic acid.
(CI 15860).

Bromocresol Green, also known as 3',3'',5',5''-tetrabromo-m-cresolsulphonphthalein.
.
Solvent Red 24, (commercially available as Atlasol Red 4B) an azo dye derived frorn 4-0-tolylazo-o-toluidine and 2-naphthol. (CI 26105).

Pigment Yellow 5 (also known as Lithol Fast Yellow Y) an azo dye derived from o-nitroaniline and 30 acetoacetanilide. (CI 11660).

~2$8755 Basic Violet 14, also };nown as Basic Fuchsine, and derived from aniline and toluidiné. (CI 42510).

Pigment Orange 2 (commercially available as Ozark Orange X-1481) an azo dye derived from o-nitro-S aniline and 2-naphthol. (CI 12060).

The flux composition was coated onto a solder preform which was then positioned within a heat-shrinkable sleeve made ~rom cross-linked polyvinylidene fluoride. A
solderable substrate, specifically an insulated wire with lO insulation removed from a segment, was inserted into the sleeve so that the uninsulated segment was positioned inside the sleeve. The sleeve was then heated causing the sleeve to shrink down onto the wire. The initial colour of the flux composition, the temperature at which the flux composition changed colour and the final colour of the flux are recorded in Table 1.

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The use of the temperature indicating solder flux composition of this invention has been described above with reference to its use in a soldering device of the heat-recoverable sleeve-t~pe. The novel temperature indicating flux composition can be used in other soldering methods, for example, hand soldering. The temperature indicating flux can be applied in the same manner as flux is usually applied in the particular soldering method, and will change colour at the critical temperature. The io flux`can be coated onto a solder preform or incorporated into the solder. It is also possible to apply the flux to the substrate(s) to be soldered.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A solder joint comprising at least two elongate substrates connected together by a mass of solder having associ-ated therewith a substantially colourless solder flux and a tem-perature indicating component and enclosed within a heat-recov-ered substantially transparent polymeric member, the temperature indicating component having changed from a coloured state to a substantially colourless state to enable the connection to be visually inspected.