WO1998021264A1

WO1998021264A1 - Viscosity defined materials for use in the fabrication of electronic assemblies

Info

Publication number: WO1998021264A1
Application number: PCT/GB1997/003088
Authority: WO
Inventors: Neil Loton; Nigel Richard Allsopp; Neil Poole
Original assignee: Multicore Solders Limited
Priority date: 1996-11-14
Filing date: 1997-11-11
Publication date: 1998-05-22
Also published as: GB9713128D0; AU4878697A

Abstract

Materials are described which have use in the fabrication of electronic assemblies. The manner of use is dependent upon chemical and physical characteristics of the materials and uses include use as a substitute for resin in soldering aids such as solid flux, cored wire, liquid flux or solder paste, in conformal coatings, in polymer thick films, in conductive inks and in adhesives. The materials are substances having a flow characteristic ranging from liquid of viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400 °C. The substance is the product of a condensation reaction between a tertiary organic base with at least one N-hydroxylalkyl group and an organic polycarboxylic acid or reactive derivative thereof. The substance is acid and has an acid number of at least 100.

Description

Viscosity Defined Materials for Use in the Fabrication of Electronic Assemblies

This invention relates to monomers, thermoplastic resins and other materials for use in the fabrication of electronic assemblies. This invention relates, more particularly to thermoplastic resins to be used in soldering aides (solid flux, cored wire, liquid flux, or solder paste) and/or conformal coatings and/or polymer thick films (PTF) and/or conductive inks and/or adhesives.

Rosin (colophony) is a natural resin derived from wood and wood by-products. It is a complex mixture of chemicals and their isomers which can vary according to feed stock, to the refining process and to the actual extraction and refining processes employed.

Nevertheless it has been used for many years in flux formulations (cored solder wire, liquids and pastes and solder pastes ) intended for soft soldering processes in the electronics assembly industry. The reasons for this use are several. The major components of rosin are carboxylic acids which are capable of dissolving the oxides and other compounds found on the surface of materials commonly soldered (copper, tin, lead). This renders the surface chemically clean and facilitates solder wetting leading to solder spread and capillary filling. Moreover, rosin molecules are large and are sterically hindered from reacting with the oxides on solder powder in solder paste at room temperature and so these products show good shelf life characteristics. During the soldering process, in which the workpiece is heated to above the melting point of the solder alloy (typically 183°C), the rosin turns from an amorphous solid into a viscous liquid. This liquid provides a physical barrier against reoxidation of the cleaned metal surfaces and serves as an effective heat transfer f luid .

Although rosin has a strong fluxing action, it is rarely sufficiently rapid or effective in its action and so small amounts of additional chemicals, commonly known as activators, are added to proprietary formulations. An advantage of rosin is that these activators are soluble in the resin melt thereby ensuring that they are effectively brought to the surfaces to be cleaned during soldering. Furthermore, the reaction products of the fluxing action of rosin and the activators are also soluble in the rosin melt and so they are effectively removed from the surface which is to be wetted by the molten solder.

Following the soldering process, rosin offers further advantages. In No Clean assembly, the residues of the process are left in situ because the low water solubility, moisture resistance and high electrical resistance of rosin mean that its retention prevents corrosion and electromigration which might compromise the functionality of a circuit. Residual activators and reaction products which are dissolved in the inert rosin matrix are also prevented from causing circuit degradation by the residual rosin.

In some applications in the electronics industry, there is a need to remove soldering flux residues and rosin can be dissolved effectively in a range of organic solvents. Since rosin protects the activators and metal salt reaction products against hydrolysis, these can also be removed in the cleaning solvents. Despite all the advantages of rosin, there are technical reasons stemming from developments in the electronics assembly industry which require further developments. As assembly processes have become more complex, they are less able to tolerate the natural variability of rosin. This is especially true of surface mount technology where the flux and solder alloy are presented to the surfaces to be joined as a paste. In an effort to achieve this consistency, many products make use of derivatives of rosin in which the material has been polymerised, hydrogenated or esterified, or subjected to combinations of these processes. While this gives improved consistency and thermal stability, variations in the chemical feed stock can still affect the properties of the flux or solder paste. With this background, flux manufacturers seeking to produce resin-based fluxes have attempted to use synthetic resins as components of soldering fluxes. An example of this is the Xersin range of materials from Multicore Solders Ltd. Also known from SU-A-1754379 is the use of a polycondensation product of ethylene glycol with maleic and phthalic anhydrides modified with castor oil (5-10 parts) and mixed with triethanolamine (90-95 parts) . The polycondensation product is a neutral polyester which does not react with the alkanolamine . However, no synthetic resins have been available which combine all of the advantages of rosin. In general they do not have an acidic component which combines the benefits of activity and long term stability in contact with metallic surfaces on an electronic assembly. The resins are generally poor solvents for activators and reaction products and they often have softening temperatures in excess of the ideal range .

Two further aims in the electronics assembly industry are the provision of fluxes with higher activity so that boards and components with poor solderability can be utilised and the requirement is avoided for lower residue levels to assist testing and inspection. One way to meet these requirements has been to use highly activated products whose residues are washed off the completed assembly using water with or without various additives. In general rosin and rosin derivatives can only be used in water washable flux formulations if they contain sufficient alkaline materials which convert them to rosin soaps which are water soluble. The compromises introduced by such formulation constraints means that the majority of solder pastes with residues which are water soluble are not based on rosins and lack the advantage of the fluxing activity and protection against oxidation which rosins confer. The lack of activity is often addressed in part by using aggressive halide activators in the formulation, but these may affect the ultimate cleanliness after soldering and cleaning. They may also adversely affect solder paste shelf life. Such halide activators may be made by neutralisation of an amine hydrohalide. This is proposed in EP-A- 0430772 which utilises neutralisation of the amine base of a di- or triethanolamine hydrohalide by tartaric acid. It is however not necessary to use the amine hydrohalide; the parent amine itself can be used,

JP-A-50021308 (Chem. Abstracts Vol. 85, No. 2. 12th July 1976, No. 947v) discloses a rosin free flux consisting of an alkanolamine (e.q. triethanolamine), neutralised by an organic acid (e.g. oxalic acid), to form a salt. A second example from Chem Abstracts C.A., 157050c (SU-A-4722973) discloses the use of neutral reaction products of C17-20 fatty acids, which are generally monomers, with triethanolamine. The neutralising reaction will prevent greening, or corrosion, as occurs with for example stearic acid.

These rosin-free or substantially rosin-free products generally also contain high molecular weight surfactants and other polyglycols which render the formulations hygroscopic. In use, the absorbed moisture causes rheological changes and adversely affects reflow behaviour. Furthermore, there are questions about the suitability of some polyglycols which may leave residues after washing which permit electro-migration to take place.

In some electronics assembly processes, moreover, there is a requirement that a post-soldering coating or filling process should be carried out to enhance electrical or mechanical performance. For example, soldered assemblies may be potted or conformally coated with a thermoplastic or thermoset resin system. Component board stand-offs may be filled with a thermoplastic or thermoset resin as an underfill. In addition, there is a developing trend to make greater use of additive circuitry and chip scale packaging which, for different reasons would bring soldering flux residues into contact with a variety of resins systems. Existing flux formulations, including those based on rosin, are not always compatible with these other resin systems and so a cleaning process is often indicated where it would not otherwise be required. According to one aspect of the present invention there is provided a substance having a flow characteristic ranging from liquid having a viscosity of 270cP to a solid having a softening point of up to 400°C preferably up to 300°C, more preferably up to 235°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N-hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid and having an acid value of at least 100, preferably at least 150, mgKOH/g.

The tertiary organic base with at least one N- hydroxyalkyl group may be a simple alkanolamine or the oleoresinous condensation product of the reaction of a tertiary organic base, which carries at least two N- hydroxyalkyl groups, with a monobasic or polybasic acid or reactive derivative thereof or combinations of these .

In a second aspect, this invention provides a method for the synthesis of such condensation product which comprises heating together the tertiary organic base with at least one N-hydroxyalkyl group and the organic polycarboxylic acid or reactive derivative thereof, the reaction conditions and/or the proportions of the reactant being such as to avoid substantially the occurrence of cross-linking reactions and to control acidity of the substance obtained to a predetermined value and molecular weight such that the reaction product has said flow characteristic.

In a third aspect, this invention provides a soldering aid which is a solid flux, a cored wire, a liquid flux or a solder paste, with which fluxing is produced by the incorporation of a substance having a flow characteristic ranging from liquid having a viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N- hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid, preferably having an acid value of at least 100, more preferably 150 mgKOH/g.

The acid substances to be discussed further herein may be monomeric, oligomeric or polymeric in nature. They are most commonly to be oligomeric or polymeric and hence are generally referred to hereinafter as resins.

The acid substances to be discussed herein are frequently novel substances but, as a group, have not hitherto been proposed for use as solder flux constituents. The acid nature of the substances, especially when they have an acid value of at least 100 mgKOH/g precludes reaction conditions between tertiary organic bases with at least one N-hydroxyalkyl group and an organic polycarboxylic acid which will result in production of an intractable cross-linked mass which would have a very low acid value. Examples of reaction products between tertiary organic bases with at least one N-hydroxyalkyl group and organic polycarboxylic acids or reactive derivatives thereof unsuitable for use in the practice of this invention are the neutral resinous reaction products of DE-A-578570. The properties of these products, as evidenced by their acid numbers, which are never higher than 60 and are generally not higher than 20, suggest that they are cross -linked and therefore insoluble in water and many organic solvents. DE-A- 831324 discloses reaction products of a bivalent or trivalent alcohol, such as diethanolamine or triethanolamine, and phthalic anhydride having an acid value of 80-100. The reactants crosslink too much when acid values obtained are too low as a result of the use of a 1:1 ratio of OH to acid groups. The product is used for stiffening felt. FR-A-1061234 discloses neutral products obtained by one stage reaction between trialkanolamines and diacids . Having regard to the ratio of reactants used in their preparation, the products obtained are clearly not acid. There is no suggestion that the neutral reaction products having at least one N-hydroxyalkyl be acidified by reaction with a polycarboxylic acid as is proposed in one embodiment of this invention. Depending on the starting materials and the reaction conditions used in the production of substances embodying this invention as well subsequent reaction at reactive groups still present therein, a variety of products having different potential uses in the fabrication of electronic assemblies may be made which embody this invention. A major benefit of some of the synthetic resins embodying this invention is that, for the first time, synthetic resins have been devised which show all the functional properties of rosin used as a soldering flux. Furthermore, by varying the monomer chain length and functionality of this family of resins, it is possible to fine tune particular attributes such as activity and softening temperature .

A highly significant benefit of some of the synthetic resins embodying this invention is that it is possible for them to be incorporated in water washable flux formulations to confer all the advantages of rosin with the additional benefit that the resin is inherently highly water soluble. No surfactants are then required in the solder paste to remove insoluble debris such as hydrolysed metal salts produced during the soldering process. The high level of acidity contributed by the resin means that additional activators, especially halide compounds are not generally required. At the same time, steric hindrance on the large resin molecules ensures that there are no unacceptable interactions between the resin in solder paste products and the solder powder. This improves storage stability of the solder paste even at room temperature.

An advantage of some of the synthetic resins embodying this invention is that they may be selected to provide characteristics which are required of both a flux and the thermoset or thermoplastic resins used in pre- or post-soldering processes. In this way it is possible to eliminate the cleaning process because compatibility can be assured. Indeed, it is possible to combine the dual functions of fluxing and potting/conformal coating or component underfill etc . in one product.

As a further refinement of the application of these novel synthetic resins to soldering processes, as aforesaid, it is even possible to complete the synthesis of these resins during an electronics assembly process. In this way, relatively low softening temperature, high fluxing power resins may facilitate a soldering process while simultaneously being reacted to produce inert, high softening point resins .

The same principles may be extended to filled resin products such as conductive adhesives and polymer thick films. By incorporating some of the synthetic resins embodying this invention in these filled resin products it is possible to confer compatibility with fluxing products using the same type of synthetic resins. The fluxing power of some of the resins described in this patent may be used in conductive adhesives where sintering of high melting point metal powders with the aid of lower melting point metal powders is intended (e.g. US Patent 5,376,403). Finally, there are other applications of rosin and chemically modified rosins which are associated with electronics assembly such as preflux coatings for protecting a metal coating on a printed circuit board (PCB) against oxidation, defluxing copper braid, surface preservatives, rework fluxes not previously discussed herein. By selecting appropriate synthetic resins embodying this invention, it is possible to substitute them for rosin and chemically modified rosins with an improvement in consistency and, in some cases, an improvement in functionality being obtained. At their simplest, the repeat units of resins embodying this invention are the reaction product of a trialkanoloamine and a cyclic anhydride of a polycarboxylic acid, or the parent polycarboxylic acid itself. Such reactions convert one of the alcohol groups of the trialkanolamine to an ester group. The amine group is unaffected, with the resultant resin containing free amine. What is generally, but not always, required is a relatively low molecular weight compound, i.e. having an average 5- to 20 repeat units. However, for coating applications it is essential that the polymer be insoluble in water and, have sufficient functionality to allow the resin to be crosslinked, or that it has a high softening point above 200°C, more preferably above 230°C. For solid flux applications in the production of printed circuit boards, it is preferred that the softening point of the resin be below 130°C. For liquid flux applications it should be soluble in a suitable solvent, preferably isopropanol (IPA). For water washable flux applications the resin should be water soluble.

In carrying out the aforesaid ester-forming reactions, use may be made of simple di-carboxylic acids such as oxalic, malonic, maleic, succinic, adipic, sebacic, tartaric, phthalic acids, as well as low molecular weight (not more than 800) polyethylene glycol (PEG) diacids, with a trialkanolamine, preferably selected from triethanolamine and triisopropanolamine, to achieve different types of reaction product. The choice of acid will depend on the nature of reaction product required as will be described hereinafter. When, for example, cross linking is required, carboxylic acids containing more than two carboxyl groups, such as pyromellitic acid, may be used as such as for example as an anhydride to leave free carboxy groups for use in crosslinking or other resin modifying reactions.

Reaction takes place merely on bringing some combinations of the two materials into intimate contact in a molten state when a pale red to yellowish brown reaction product is formed. Colour increases in intensity with molecular weight. Alternatively, reaction can be carried out in solution using an inert high boiling solvent . The carrying out of the reaction in solution may be harnessed to the formation of the resin _.in situ in the production of coatings, soldering fluxes and solder pastes. The reaction product obtained in either case contains both a free acid group or acid derivative and has free amine functionality. The simplest monomers which embody this invention which may be prepared have a relatively high viscosity. This viscosity drops if there is further reaction as hydrogen bonding is reduced. The reaction products may then have too low a viscosity. Further reaction will generally lead to a more viscous liquid or softenable solid product as molecular weight increases further. In general, the acid used in the production of the resin may be an aliphatic or aromatic acid and it may contain any of a variety of different functional groups. Preferably the acid possesses the general formula R - (C0Y)_n wherein R is a chemical bond or an aliphatic or aromatic group optionally substituted by alkoxy, aryloxy, alkylcarbonyl, aryl, or hydroxy, in addition to COY, Y is OH, a halogen atom, or an esterifying group, or two moieties COY together form a carbonyloxycarbonyl group, and n is an integer from 2 to 4.

The tertiary organic base with at least one N- hydroxyalkyl group will preferably possess the general formula

^NR1^R2^R3

wherein R-,, R2 and R3 are, independently of one another, alkyl optionally substituted by hydroxyl, alkoxy, aryloxy, alkoxycarbonyl , or aryl groups, with at least one of R-^, R₂ and R₃ being hydroxyalkyl , or be the oleoresinous condensation product of a tertiary organic base, which carries at least two N-hydroxyalkyl groups, with monobasic or polybasic acids or reactive derivatives thereof or combinations of these, the condensation product containing at least one N- hydroxyalkyl group. Preferably, the tertiary organic base with at least one N-hydroxyalkyl group is triethanolamine or triisopropanolamine or the condensation product of triethanolamine or triisopropanolamine with a dicarboxylic acid or acid anhydride.

Of particular interest with resins embodying this invention is their ability to undergo modification of their resin properties, whereby the resin can have a range of properties from a viscous liquid to a high melting point solid. This can be achieved by changing the backbone of oligomers and polymer resins by use of trace amounts of other copolymers/monomers and/or by inclusion of pendant groups. Water solubility can be conferred on the resin by inclusion of hydrophilic substituents and or by having hydrophilic moieties interrupt one or more hydrocarbon groups in R and Y. This objective can be met by use of short chain di-carboxylic acids C2 to Cg, i.e. R is C₀-C^ or alkoxy-carboxylic diacids for the backbone, or by the presence of hydrophilic pendant groups such as acid and alcohol groups. The free amine groups in the chain will be hydrophilic, for example when triisopropanolamine (TIPA) has been reacted with maleic acid.

If water solubility is not required, then the resin can be made water insoluble by having pendant groups which are hydrophobic, such as long chain aliphatic groups (greater than C-^_Q), or alkyl ester groups, or by use of hydrophobic main backbone groups in oligomers or polymer resins. These hydrophobic oligomers or polymers may be obtained for example if the tertiary organic base with at least one N- hydroxyalkyl group is derived from the condensation product of a trialkanolamine with long carbon chain diacids ( C6 or higher ) , for example by reaction of triisopropanolamine with adipic acid.

If a high softening point material is required, then the resin can be made as an oligomer or polymer with a rigid backbone using a tertiary organic base with at least one N-hydroxyalkyl group which is the condensation product of a trialkanolamine such as triethanolamine with long chain dicarboxylic acids (>Cg) or aryl polycarboxylic acids such as terephthalic acid or by using monomers which provide high molecular weight pendant groups and a branched alkanolamine such as triethanolamine (TEA). Increasing the molecular weight (degree of polymerisation), will also increase the softening point. This is achievable when reacting triethanolamine (TEA) with phthalic acid. Resins embodying the invention that are liquid at ambient temperature, which allows their use without solvents in formulations, can be made by including flexible segments into the backbone of the chain, as when the tertiary organic base with at least one N- hydroxyalkyl group in the condensation product or a trialkanolamine and a low molecular weight ( less than 800) polyethylene glycol (PEG) dicarboxylic acids.

The inclusion of pendant functional groups in the oligomer and polymer resins can facilitate high temperature self crosslinking to form a thermoset resin. For example, the resin may be the reaction product of a dicarboxylic acid and a trialkanolamine, with residual hydroxy groups in the polymer having been reacted with a monocarboxylic acid, dicarboxylic acid, or acid anhydride or a combination thereof. Examples of compounds to use for this purpose are maleic anhydride, phthalic anhydride, stearic acid, montanic acid, sebacic acid, acetic anhydride and combinations thereof. Crosslinking of the resin can also be facilitated by the inclusion of dedicated crosslinkers such as urea-formaldehyde (UF) and melamine- formaldehyde (MF) reaction products.

Resins embodying this invention can be used for a variety of different applications depending upon their chemical and physical properties. Resins may be prepared for use as water borne surface coatings (alone or in combination with MF and UF crosslinkers ) for metals and wood, as fluxing agents in solid fluxes, cored wire used in soldering and brazing, in liquid fluxes and solder pastes, in etchants and as crosslinking agents. The resins can remain water soluble after subsequent processing. For example they can provide temporary protective coatings, and they can provide water soluble post soldering residues. When the resins are water insoluble after processing, they may serve as permanent coatings, and as "No-clean" post soldering residue fluxes. Resins embodying this invention which can be crosslinked can be used, in particular, in the production of conformal coatings and PTF ' s and conductive inks and adhesives . The following examples illustrate the invention.

In the examples acidic resins embodying the invention were produced by a series of temperature mediated acid/aminoalcohol reactions. The synthesis of polymeric aminoalcohols used to produce polymer resins is also illustrated. In the examples the following abbreviations are employed:

TEA = Triethanolamine, TIPA = triisopropanolamine, MA = malonic acid, SA = sebacic acid, MAn = maleic anhydride, PAn = phthalic anhydride, IPA = isopropanol. Example 1 Preparation of an acidic amine monomer resin

The following two procedures illustrate the condensation of tertiary organic bases with at least one N-hydroxyalkyl group with an organic polycarboxylic acid or reactive derivative thereof where the organic base is a trialkanolamine and the acid is a simple diacid.

la) An acidic liquid monomer resin was produced by the heat mediated reaction of TEA with MAn mixed in equimolar proportions. 30g of TEA and 20g of MAn were heated together to a temperature of 60°C when they were vigorously stirred until melting was complete. The mixture was allowed to cool when it produced a pale yellow viscous liquid.

The acid value of the reaction product was found to be 220-230 mgKOH/g compared with a theoretical value of 227. A small quantity of the liquid resin was dripped onto a ring of solder wire placed on a flat copper coupon. When the coupon was floated on a solder bath at 235 °C, the solder ring melted and wetted the surface of the copper coupon demonstrating the fluxing action of the liquid monomer resin. When the copper coupon was cold, the organic residues on the reflowed solder ring were removed by rinsing in cold water.

lb) An acidic solid monomer resin was produced by the heat mediated reaction of an equimolar mixture of TIPA (30g) and MAn (15g) in the manner described in Example la. This time, the product was a friable yellow solid with an acid value of 188-192 mgKOH/g compared with a theoretical value of 194 mgKOH/g. It showed the same fluxing action and water solubility of residues as Example la when used to reflow a ring of solder wire placed on a copper coupon. Example 2

The following two procedures illustrate the preparation of an oligomer ternary organic base with at least one N-hydroxyalkyl group (neutral polymer backbone ) .

General

A dicarboxylic acid and a trialkanolamine were reacted. The two reactants were mixed in a mole ratio of 0.9-0.95:1 dicarboxylic acid: alkanolamine (the alkanolamine should always be in excess to minimise crosslinking of the backbone into an intractable mass). The progress of the reaction could easily be followed by measuring the acid value for the mixture; as reaction progresses the acid value falls. During reaction the colour of the mixture changed and became darker and the viscosity of the mixture increased.

2a) Malonic acid and triethanolamine (a) For a MA/TEA mixture an initial reaction temperature of 100°C was used to prevent thermal breakdown of the MA. When the acid value had fallen to below half its starting value, then the temperature was increased to 120°C for the remainder of the reaction. Reaction was 95% complete after 16 hrs. The progress of the reaction is shown in Table 1.

Table 1

Acid Values for MA/TEA Reaction Profile

2b) Malonic acid and triisopropanolamine

For MA/TIPA, the reactants were mixed and held at 120°C for 1 hour, 135°C for 1 hour, 150°C for 21/2 hours. This yields a viscous water soluble liquid with an acid value of 50.5 mgKOH/g ( 83.6% complete reaction) .

Example 3 Preparation of acidic amine polymer resins

The following three procedures illustrate the condensation of tertiary organic bases with at least one N-hydroxyalkyl group with an organic polycarboxylic acid or reactive derivative thereof where the organic base is an oligomer of the type described in Example 2 and the acid is a diacid or anhydride.

General

The reaction is achieved by mixing the oligomer prepared in Example 2 with dicarboxylic acids, or reactive derivatives thereof. The two materials are mixed in a ratio of 1 mole of acid or acid derivative per repeat unit of the oligomer. The ratio is chosen to minimise unwanted crosslinking of the backbone. The reaction is achieved by heating the material until reaction takes place. During reaction the viscosity of the liquid will increase, for some dicarboxylic acids the reaction is catalysed by inclusion of a catalyst (solid NaOH).

3a) Product of Example (2b) and phthalic anhydride For a mixture of the condensation product of

MA/TIPA with PAn the reaction is carried out at 80°C, for 15 minutes when the reaction is complete. During reaction the liquid viscosity increases, no visible change in colour is observed. The resultant resin has an Acid Value of 145 mgKOH/g. The resin is only partially soluble in water.

3b) Product of Example 2(a) and sebacic acid

For a mixture of the condensation product of MA/TEA with SA the reaction is carried out at 180°C with NaOH as a catalyst, the reaction is allowed to take place for approximately 30 minutes, when the mixture is allowed to cool. The resultant resin has an acid value of 140 mgKOH/g. The resin is insoluble in water.

3c) Product of Example 2(a) and maleic anhydride

For a mixture of the condensation product of MA/TEA with MAn the reaction is carried out at 60°C, for 15 minutes when the reaction is complete. During reaction the liquid viscosity increases and no visible change in colour is observed. The resultant resin has an Acid Value of 200 mgKOH/g. The resin is soluble in water.

3(d) Product of Example 2(b) and maleic anhydride

For a mixture of the condensation product of MA/TIPA with MAn, the reaction is carried out by slowly adding the MAn to a stirred beaker of MA/TIPA at 75 °C. Viscosity increased as the esterification reaction proceeded and once addition was complete, the mixture was allowed to cool to room temperature. The product was a soft, sticky, water soluble solid which became a harder resin at -5°C. The acid value was 209 mgKOH/g.

Example 4 Liquid Flux Formulation (water soluble)

The resin prepared in Example 3 (c) was used to prepare a liquid flux, by combination with a suitable solvent and the addition of an optional activator. The resin was thinned with IPA to give a suitable viscosity for application to circuit assemblies and the activator added as follows.

Component Weight % Content (by weight)

Resin example 3(c) 25g 10

Succinic Acid 2.5g 1%

IPA (solvent) 222.59 89%

The formulation was prepared at ambient temperature by weighing out each of the components set out above into a glass bottle. After the lid had been closed the bottle was vigorously shaken until the components were dissolved, in the solvent, to produce the desired flux formulation. The flux was applied to a populated printed circuit board (pcb) and processed in a commercial wave soldering machine. The flux produced good shiny soldered joints with minimal defects. After wave soldering the resides remaining on the PCB could be easily removed by washing in cold water.

Example 5 Liquid Flux Formulation (No-Clean)

A second liquid flux was prepared using the procedure in Example 4, but using the resin prepared in Example 3(b). The resin was mixed with solvent and an optional diamine, to facilitate crosslinking of the resin residues during soldering, in order to make a no-clean liquid flux.

Component Weight % Content by weight

Resin example 3(b) 25g 10%

Diethylene triamine 2.5g 1%

IPA (solvent) 222.5g 89%

The formulation was prepared at ambient temperature by weighing out each of the components into a glass bottle. After securing the lid, the bottle was vigorously shaken until the components were dissolved in the solvent. The flux thus produced was applied to a PCB and processed in a commercial wave soldering machine producing good, shiny soldered joints with minimal defects.

The flux will undergo a crosslinking reaction when in contact with the solder wave to yield benign post soldering residues. The resultant residues being inert as measured by a CM11 Contaminometer. As an alternative to the dia ine, MF and UF crosslinking agents can be utilised.

Example 6 Solder Paste Flux Medium Formulation (Water

Washable)

The resin prepared in Example 1(b) was used to prepare a solder paste by combination with rheology modifying agents and solvent to form a solder paste flux medium and mixing this with solder powder. The components used in making up a typical formulation were: Component % Content by weight

Sample resin 1(b) 60% Dalpad A ( solvent-ethylene glycol monophenylether ) 35%

Low molecular weight PEG wax (rheology modifier) 5%

Mixing of the ingredients took place with a high shear mixer in a beaker on a hotplate until a clean solution was obtained (80°C). The mixture was stirred as it cooled rapidly to ambient temperature.

The cold flux medium (11%) by weight was mixed with Sn63 solder powder (89% by weight) conforming to the JSTD-004 size specification Type 3. The properties of the resulting solder paste were as follows:

Properties of Solder Paste made from Example 6 Flux

Viscosity 950,00 cP

Printing Good

Solder balling Pass

Spread factor 96.1% Residue solubility in water Good

Example 7 Solder Paste Flux Medium Formulation (water washable)

The resin prepared in Example 3(d) was used to prepare a solder paste by combination with rheology modifying agents and solvent to form a solder paste flux medium and mixing this with solder powder. Component % Content by Weight

Sample Resin 3(d) 55 TIPA (rheology modifier) 20

Low molecular weight PEG wax (rheology modifier) 10 Dalpad A (solvent) 15

The ingredients were mixed in the manner described in Example 6 and a solder paste was made using the same solder powder ( 89% by weight ) . The properties of the resulting solder paste were as follows:

Properties of Solder Paste made from Flux of Example 7

Viscosity 980,00 cP

Printing Good

Solder Balling Fair Residue Solubility in water Good

Example 8 Conformal Coating Formulation

Sample resin 3(d) produced in the foregoing Example 3(d) can be used for surface coatings, including conformal coatings, by combination with a suitable crosslinking agent such as MF or UF resin. To lower the viscosity of the resultant mixture, a suitable solvent could be included.

Component Weight % Content(by weight)

Sample Resin 3(d) 60g 50%

Cymel 385 24g 20% (a MF crosslinking agent form Dyno-Cytec)

Dalpad A (solvent) 36g 30% The formulation was prepared at ambient temperature in a glass beaker. The components were weighed into the beaker and manually mixed with a spatula until a homogeneous solution was achieved.

The formulation was applied to a circuit assembly by brushing, and cured at 145°C for 35 minutes. Curing could be speeded up by use of a suitable weak organic acid catalyst such as Cycat 296-6 from Dyno-Cytec.

Claims

1. A substance having a flow characteristic ranging from liquid having a viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N-hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid and having an acid number of at least 100.

2. A substance as claimed in claim 1 which is an oligomer or polymer resin.

3. A substance claimed in claim 1 or claim 2, wherein the organic polycarboxylic acid possesses the general formula

R - (COY)_n wherein R is a chemical bond or an aliphatic or aromatic group optionally substituted by alkoxy, aryloxy, alkylcarbonyl, aryl, or hydroxy in addition to COY, Y is OH, a halogen atom, or an esterifying group, or two moieties COY together form a carbonyloxycarbonyl group, and n is an integer from 2 to 4.

4. A substance as claimed in claim 3 wherein the acid is selected from oxalic acid, malonic acid, tartaric acid, maleic acid, succinic, acid, adipic acid, sebacic acid, phthalic acid, polyethylene glycol diacid, and pyromellitic acid, and combinations thereof .

5. A substance as claimed in claim 1, 2, 3 or 4 , wherein the tertiary organic base with at least one N- hydroxyalkyl group is a trialkanolamine.

6. A substance as claimed in claim 1, 2, 3 or 4 wherein the tertiary organic base with at least one N- hydroxyalkyl group is the oleoresinous condensation product of the reaction of a tertiary organic base which carries at least two N-hydroxyalkyl groups with a monobasic or polybasic acid or a combination thereof.

7. A substance as claimed in any preceding claim which additionally contains hydrophilic substituents and/or has hydrophilic moieties interrupting one or more of the hydrocarbon groups comprised by R and Y.

8. A substance as claimed in claim 6, wherein the aminoalcohol comprises at least two hydroxyalkylene groups that contain up to four carbon atoms each.

9. A substance resin as claimed in any of claims 1 to 6 and 8, which comprises hydrophobic pendant and/or main backbone groups.

10. A substance as claimed in claims 1 and 2, which is solid at ambient temperature and the tertiary organic base with at least one N-hydroxyalkyl group is triethanolamine or triisopropanolamine and the acid is a long chain (C6 or greater) aliphatic polycarboxylic acid or an aryl polycarboxylic acid.

11. A substance as claimed in claims 1 and 2, which is liquid at ambient temperature and in which the acid used is a short chain (C5 or less) dicarboxylic acid or low molecular weight polyethylene glycol dicarboxylic acid.

12. A substance as claimed in claims 1, 2 and 6 which is the reaction product of the condensation product of a dicarboxylic acid and a trialkanolamine, having residual N-hydroxyalkyl groups and a monocarboxylic acid, dicarboxylic acid, or acid anhydride, or combination thereof.

13. A substance as claimed in claim 12, wherein residual hydroxyl groups are reacted with maleic anhydride, phthalic acid, stearic acid, montanic acid, sebacic acid, acetic anhydride or combinations thereof.

14. A substance as defined in claim 12 wherein the trialkanolamine is triethanolamine or triisopropanolamine.

15. A method for the production of a substance as claimed in any of claims 1 to 14 which comprises heating together a tertiary organic base with at least one N-hydroxyalkyl group and the organic polycarboxylic acid or reactive derivative thereof, the reaction conditions and/or the proportions of the reactants being such as to avoid substantially the occurrence of cross-linking reactions and to control acidity of the substance obtained to a predetermined value and molecular weight such that the reaction product has said flow characteristic.

16. A method as claimed in claim 15, wherein the reaction is carried out in the melt.

17. A method as claimed in claim 15 or 16, wherein the tertiary organic base with at least one N- hydroxyalkyl group is the oleoresinous condensation product of a tertiary organic base which carries at least two N-hydroxyalkyl groups with a monobasic or polybasic acid or reactive derivative thereof or combination of these, the condensation product containing at least one N-hydroxyalkyl group.

18. A soldering flux composition which is a solid flux comprising a fluxing agent which is a solid substance having a softening point of up to 400°C and which is the product of a condensation reaction between a tertiary base with at least one N-hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof, which product is acid.

19. A soldering flux composition which is present as the core of a cored wire comprising a fluxing agent which is a substance having a viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N-hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid.

20. A soldering flux which is a liquid flux comprising fluxing agent which is a substance having a viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N- hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid.

21. A soldering flux which is a solder paste comprising a fluxing agent which is a substance having a viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N- hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid.

22. A conformal coating composition on or for use on an electronic assembly which comprises a substance as defined in any one of claims 1 to 15.

23. A PTF, conductive ink or electrically and/or thermally conductive adhesive composition which comprises a substance having a viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N-hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid.

24. A PTF, conductive ink or conductive adhesive as claimed in claim 23, which comprises a sinterable high melting point metal powder in conjunction with a lower melting point metal powder.

25. An underfill composition, a preflux coating for protecting a metal coating on a PCB against oxidation or a defluxing braid which comprises a substance having a viscosity of more than 270 cP at ambient temperature to a solid having a softening point of up to 400°C, the substance being the product of a condensation reaction between a tertiary organic base with at least one N-hydroxyalkyl group and an organic polycarboxylic acid or reactive derivative thereof and being acid.

26. A composition as claimed in any one of claims 18 to 25, wherein said substance has an acid value of at least 100 mgKOH/g.