GB2110204A - Perfluoro(alkylcyclohexane) mixtures for use in vapour soldering - Google Patents

Abstract

An evaporable fluid, for use principally in vapour-soldering applications, comprises a mixture of perfluoro (alkylcyclohexanes) having from 12 to 17 carbon atoms in their molecules, the mixture having a boiling range within the limits 180 DEG - 300 DEG C. The fluid may be produced by fluorinating a narrow-cut linear alkylbenzene with CoF3.

Description

SPECIFICATION Novel fluorocarbon fluids This invention relates to novel perfluorocarbon fluids which are useful, inter alia, as hydraulic fluids and may be used in vapour soldering applications on electronic components e.g. printed circuit boards.

There is a need for a high-boiling, chemically-inert fluid for use in such applications, which will be neither degraded by heat nor decomposed by contact with metallic or polymeric materials at elevated temperatures.

According to this invention we provide a fluid comprising a liquid mixture of saturated perfluorocarbons composed of at least two perfluoro(alkylcyclohexanes) having between 12 and 17 carbon atoms (inclusive) in the molecule and having a boiling range within the limits 180 -300 C.

Preferably the boiling range is in the range 200 -270 C. More preferably it is 200 -250 C.

Preferably the fluid contains a mixture of perfluoro(alkylcyclohexanes) selected from fluorocarbons containing 12, 13, 14,15, 16 and 17 carbon atoms in their molecules. The molecularformulae of such compounds are; (1) C12F24 Perfluorohexylcyclohexane (2) C13F26 Perfluoroheptylcyclohexane (3) C14F28 Perfluorooctylcyclohexane (4) C15F30 Perfluorononylcyclohexane (5) C16F32 Perfluorodecylcyclohexane (6) C17F34 Perfluoroundecylcyclohexane Of the compounds listed above it is believed that (2), (4), (5) and (6) are novel compounds per se.

The fluids according to the invention are conveniently prepared by the cobaltic fluoride fluorination of known hydrocarbon materials (such as those used in the production of linear alkylbenzene sulphonate surfactants) which may be represented by formula:

The cobaltic fluoride fluorination of hydrocarbons is well described in, for example, the paper by Barbour, Barlow and Tatlow in Journal of Applied Chemistry 1952,2, pages 127-133 and a typical apparatus for such a fluorination reaction is shown on page 130 of this paper, together with an account of the fluorination procedure.

Alternatively the fluorination may be carried out in a fluidised-bed reactor as taught in British patent specification 1,281,822 wherein the fluorinating agent, in solid particulate form, is fluidised by means of a mechanical stirrer and the hydrocarbon to be fluorinated and elemental fluorine are passed simultaneously into the fluidised bed of fluoride particles, to produce a fluorinated hydrocarbon product.

In general, fluids according to the invention are note-worthy for high thermal anc chemical stability and the ability not to degrade in the presence of metals even at temperatures above 200 C.

The condensation reflow soldering technique in which fluids according to the invention may be applied is described (inter alia) in U.S. patent specification 3,866,307 and U.S. Re-issue patent 30,399. In this application the fluid would be heated to vapour form before use. Liquid-phase or phase-change applications are also possible e.g. in heat transfer and hydraulic fluid contexts as di-electric fluids in transformers and switchgear, as working fluids for heat engines, as manometric liquids, and as fluids for use under pressure. It is also possible that the oxygen-carrying and emulsification properties of fluids of the inventon could lead to them being useful as blood plasma substitutes.

The invention will now be further illustrated by reference to the following data on the preparation and physical properties of examples of fluids according to this invention.

In a typical fluorination reaction 15.65 Kg of DOBANE 80* (Average M.W.211) were passed through a stirred reactor containing CoF3 at 330"C to give 47.13 Kg. of fluorinated liquid product. After fractionation and purification this yielded 21.21 Kg of a mixture of perfluoroalkylcyclohexanes as a dense colourless liquid with a boiling range of 217-243 C.

The physical properties of the fluorinated produce were as follows: Boiling range 217 -243 C Pourpoint -45 C Specific gravity 1.987 * A narrow-cut linear alkylbenzene of formula;

with the alkyl chain predominantly Cg, C10.

The utility of the fluids according to this invention will be further illustrated by reference to the following test data obtained by using such a fluid in the vapour-soldering application described in U.S. patent 3,866,307.

In the following tests the vaporised fluid used (designated "the fluid") was a mixture of perfluorinated (alkylcyclohexanes) having a boiling range of approximately 217 -243 C.

Test 1 An integrated circuit was soldered to a board using 'doughnut-ring' preforms made of Alpha+ Solder Sn/Pb 63/37. Dwell time in the fluid vapour was 10 seconds. Solder M.Pt. ca. 185"C. Some good fillets were obtained.

Test2 Using Multicore++ non-slump solder, designated Sn62 Pr AB3, XM 27.33, to fix a chip carrier to a plated ceramic substrate. Dwell time in the fluid vapour was 10 seconds. Solder M.Pt. ca 185 C. Good solder fillets were formed.

Test 3 Using a higher melting point solder (221"C), 96.5/3.5 Sn/Ag alloy, supplied by Alpha+ Metals, to fix a chip carrier to a ceramic substrate. At 30 seconds dwell time in the fluid vapour a reasonable fillet was obtained.

Test 4 Using Alpha+ 'vapour phase' solder 62/36/2 Sn/Pb/Ag, M.Pt. 1790C to solder a chip carrier onto a plated ceramic substrate. Dwell time 10 secs. Soldering was satisfactory.

+ Alpha is the trade name of Alpha Metals Ltd., Hodford House, High Street, Hounslow, Middlesex, England.

++ Multicore is the trade name of Multicore Solders Ltd., Westbury, NY 11590, U.S.A.

Test 5 A plated ceramic substrate, without solder plate, was immersed in the fluid vapour. No pad damage occurred.

Test 6 A plain board having Sn/Pb 60/40 coated tracks was reflowed satisfactorily by immersing the board for 10 seconds in the fluid vapour.

Test 7 Photo-resist compatibility test. No damage occurred to the epoxy photo-resist during several immersions in the fluid vapour.

Test 8 Resistors fitted with solder preforms were satisfactorily fixed to a test board.

CLAIMS (Filed on 17 Nov. 1982) 1. An evaporablefluid comprising a liquid mixture of saturated perfluorocarbonscontaining at least two perfluoro-(alkylcyclohexanes) having between 12 and 17 carbon atoms in the molecule and having a boiling range within the limits 180 - 300 C.

2. A fluid as claimed in claim 1 which has a boiling range within the limits 2000 to 270 C.

3. A fluid as claimed in claims 1 or 2 which has a boiling range within the limits 200 to 250 C.

4. A fluid as claimed in claims 1,2 or 3 which contains a mixture of perfluro(alkylcyclohexanes) selected from those containing 12, 13, 14, 15, 16 and 17 carbon atoms in their molecules.

5. Perfluoro(helptylcyclohexane) C13F2s 6. Perfluoro(nonylcyclohexnane) C15F30 7. Perfluoro(decylcyclohexane) C1eF32 8. Perfluoro(undecylcyclohexane) C17F34 9. A process for preparing a fluid as claimed in claim 1 wherein a hydrocarbon of the general formula

is fluorinated by reaction with a higher metal fluoride.

10. A process as claimed in claim 9 wherein the higher metal fluoride is cobaltic fluoride.

11. A method of soldering electrical components comprising immersing electrical components incorporating solder preforms in the vapour of a fluid as claimed in claim 1, melting the solder to solder the components together or to circuit elements and then removing the components from the fluid vapour and allowing them to cool.

12. An evaporable fluid comprising a liquid mixture of saturated perfluorocarbons substantially as hereinbefore described with reference to the description in the specification.

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

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. Test 8 Resistors fitted with solder preforms were satisfactorily fixed to a test board. CLAIMS (Filed on 17 Nov. 1982)

1. An evaporablefluid comprising a liquid mixture of saturated perfluorocarbonscontaining at least two perfluoro-(alkylcyclohexanes) having between 12 and 17 carbon atoms in the molecule and having a boiling range within the limits 180 - 300 C.

2. A fluid as claimed in claim 1 which has a boiling range within the limits 2000 to 270 C.

3. A fluid as claimed in claims 1 or 2 which has a boiling range within the limits 200 to 250 C.

4. A fluid as claimed in claims 1,2 or 3 which contains a mixture of perfluro(alkylcyclohexanes) selected from those containing 12, 13, 14, 15, 16 and 17 carbon atoms in their molecules.

5. Perfluoro(helptylcyclohexane) C13F2s

6. Perfluoro(nonylcyclohexnane) C15F30

7. Perfluoro(decylcyclohexane) C1eF32

8. Perfluoro(undecylcyclohexane) C17F34

9. A process for preparing a fluid as claimed in claim 1 wherein a hydrocarbon of the general formula

is fluorinated by reaction with a higher metal fluoride.

10. A process as claimed in claim 9 wherein the higher metal fluoride is cobaltic fluoride.

11. A method of soldering electrical components comprising immersing electrical components incorporating solder preforms in the vapour of a fluid as claimed in claim 1, melting the solder to solder the components together or to circuit elements and then removing the components from the fluid vapour and allowing them to cool.

12. An evaporable fluid comprising a liquid mixture of saturated perfluorocarbons substantially as hereinbefore described with reference to the description in the specification.