Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K1/00—Soldering, e.g. brazing, or unsoldering
  • B23K1/08—Soldering by means of dipping in molten solder
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K1/00—Soldering, e.g. brazing, or unsoldering
  • B23K1/0008—Soldering, e.g. brazing, or unsoldering specially adapted for particular articles or work
  • B23K1/0016—Soldering of electronic components
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/38—Selection of media, e.g. special atmospheres for surrounding the working area
  • B23K35/386—Selection of media, e.g. special atmospheres for surrounding the working area for condensation soldering
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C43/00—Ethers; Compounds having groups, groups or groups
  • C07C43/02—Ethers
  • C07C43/03—Ethers having all ether-oxygen atoms bound to acyclic carbon atoms
  • C07C43/04—Saturated ethers
  • C07C43/12—Saturated ethers containing halogen
  • C07C43/126—Saturated ethers containing halogen having more than one ether bond

Definitions

• a preferred method for soldering a series of joints is to immerse' the pre-positioned components into a vapor bath which is sufficiently hot to melt the solder.
• the latent heat of vaporization causes the solder to melt as the vapors condense on the cool surfaces.
• solders Preferabl , solders
• ⁇ j _5 condenses primarily on the cooler components having a large thermal capacity. Even heating minimizes polymer degradation and produces a finished product that is clean and has minimal metal oxidation. Vapor phase soldering, for these reasons, is becom-
• perfluoropoly- ether, perfluoroheptaglyme, CF,0(CF_CF 2 0) 7 CF_ can be used as a vapor-phase soldering fluid and offers several advantages in this capacity over the prior art vapor-phase soldering fluids.
• the most notable advantages are: (1) Because perfluoroheptaglyme does not have more than two sequential difluoro ethylene units, the likelihood of producing deadly perfluoroiso- butylene while refluxing is greatly diminished (time-weighted average threshold limit for an 8-hour day is 0.01 ppm). No evidence of perfluoroisobuty- lene was found using a state-of-the-art gas chromatographic technique.
• Perfluoroheptaglyme is superior to low molecular weight oligo ers of hexafluoropropylene oxide such as those described by Dishart and the copolymers of hexafluoropropylene oxide and difluoromethylene oxide described by Briggs since it is a unimolecular fluid.
• the composition of a fluid consisting of a mixture of components having different molecular weights is always changing as the more volatile components evaporate thus giving a fluid with a higher boiling point with time.
• Perfluorheptaglyme is superior to the perfluoropentaglyme described by Calini and Modena since its boiling point of 205"C is better suited for solders presently being used in the industry.
• Diethylene glycol monomethyl ether can be reacted with sodium metal to form an alcoxide which can then be reacted with 1,2-bis(2-chloroethoxy)- ethane to form heptaglyme.
• triethylene glycol mono- methyl ether can be reacted with thionyl chloride to replace the hydroxyl group with chlorine which can then be reacted with the alkoxide formed in the reaction of tetraethylene glycol monomethyl ether with sodium.
• the heptaglyme can be easily distilled at reduced pressure to obtain a pure product.
• the heptaglyme is then perfluorinated preferab ⁇ ly by direct fluorination techniques. Because of the reactive nature of elemental fluorine, it is beneficial to dilute the fluorine with an inert gas such as nitrogen or 'helium. Typically, the fluorine is diluted with nitrogen and as higher degrees of fluorination are achieved, the concentration of fluorine is usually increased. Due to the extreme exothermicity of the reaction, the fluorination must be carried out slowly unless provisions have been made for rapidly removing the heat of reaction. Submersion of the reactor in a cooled liquid bath is usually adequate for achieving commercially ac ⁇ ceptable rates of reaction.
• the fluorination reaction is generally carried out at a temperature between about -80 and about +200"C, preferably between -20 and +20 * C. It can be carried out in a reactor containing an ultraviolet radiation source or in the dark. Using the pre ⁇ ferred temperature range, it is not necessary to have an ultraviolet light source since the fluorine is sufficiently reactive. If an ultraviolet light source is used, a wavelength between 250 and 350 nm is preferred. When the reactor is radiated with an external light source, a transparent window is needed which does not react with either fluorine or hydrogen fluoride. A quartz lens coated with a thin film of fluorinated ethylene-propylene copolymer works well.
• the fluorination reaction can be carried out in a variety of ways .
• the heptaglyme can be coated on an inert solid such as sodium fluoride powder to give a free-flowing powder which can be fluorinated in either a stationary tube, in a rotating drum-type reactor, or in a fluidized bed.
• the yields associ ⁇ ated with such reactions are generally poor due to the abundance of side reactions which give primarily higher molecular weight branched products.
• the reaction can be carrier out either in a batch mode where all of the heptaglyme is dissolved in the solvent prior to fluorination or in a continuous mode where heptaglyme is continuously being pumped into the solvent as fluorine is being bubbled through solution.
• the continuous operation gives a prefer- red yield, better product quality, and improved rates.
• a hydrogen fluoride scavenger such as sodium fluoride may or may not be present in the solution to scav- enge the by-product hydrogen fluoride.
• the preferred mode for carrying out the reaction is with a sufficient quantity of sodium fluoride being present to complex with all of the hydrogen fluoride formed.
• perfluoroheptaglyme is preferably prepared by continuously introducing heptaglyme into a stirred reactor containing a solvent, such as 1, 1 ,2-trichlorotrifluoroethane, which is maintained between about -20 and about +20'C.
• Dilute fluorine gas is the preferred fluorinating agent and reacts well in the absence of ultraviolet radiation.
• the fluorine is diluted so that it is below the flamm ⁇ able limits of the liquid medium (in fluorine) .
• Superior yields are obtained when sufficient quanti ⁇ ties of sodium fluoride are present to complex all of the by-product hydrogen fluoride.
• the product produced in this manner generally has a purity between 90 and 95% with a residual hydrogen content of 0.001% or less.
• a component to be soldered is immersed in a perfluoroheptaglyme vapor bath to melt the solder. Soldered components are then removed from the bath.
• a preferred solder is 60/40 tin/lead (Sn/Pb) solder, but generally any solder which has a melting point below about 200"C can be used. The method is particularly useful for soldering electrical com ⁇ ponents to printed circuit boards.
• Example 3 Fluorination of Heptaglyme in a Batch- Type Solvent Reactor A mixture of 200.6 g of heptaglyme, 4 liters of 1, 1,2-trichlorotrifluoroethane and 800 g of sodium fluoride powder was placed in a 2 foot long aluminum reactor which was constructed from 10" pipe. The reactor was rotated at approximately 60 revolutions per minute in a water/ethylene glycol bath which was held at -10'C. The reactor was flushed with nitro ⁇ gen for several hours prior to beginning the fluorination.
• a gas flow of 400 cc/min fluorine and 800 cc/min nitrogen was maintained for 14 hours, then the fluorine and nitrogen flows were reduced to 300 and 600 cc/min, respectively, for an additional 5 hours during which time the reactor was slowly heated to 70"C.
• the contents of the reactor were exposed to pure fluorine at 70 * C overnight (12 hours) before cooling to room temperature and flushing with several volumes of nitrogen.
• the contents of the reactor were filtered and the NaF was washed several times with approximately 3 liters of 1, 1 ,2-trichlorotrifluoroethane.
• the exit gas of the reactor was monitored throughout the reaction to ensure that an adequate amount of fluorine was being delivered to completely fluorinate the incoming heptaglyme. Typically, the exit gas contained approximately 5% fluorine which indicated that a slight excess of fluorine was being used.
• the contents of the reactor were filtered following the reaction. The insoluble portion of the mixture was washed with several liters of 1, 1 ,2-trichlorotrifluoroethane. The filtrates were combined and distilled to give 428 g of a fluorocarbon fluid. Treatment of the fluid at 175 * C with 50% fluorine gave a fluid of similar weight which was essentially free of any hydrogen. A second distillation resulted in the isolation of 396 g of perfluoroheptaglyme (57% yield) .
• Example 6 Test Soldering of Electronic Components with Perfluoroheptaglyme An evaporation tank was filled to its normal operating level with perfluoroheptaglyme. After achieving a controlled reflux, a circuit board containing three integrated circuits was lowered into the vapor zone for 25 seconds. The following chips were successfully soldered:

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Electric Connection Of Electric Components To Printed Circuits (AREA)
• Molten Solder (AREA)

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• 1989
  • 1989-09-28 EP EP89911313A patent/EP0436635A1/de not_active Withdrawn
  • 1989-09-28 JP JP1510560A patent/JPH04503187A/ja active Pending
  • 1989-09-28 KR KR1019900701118A patent/KR900701455A/ko not_active Withdrawn
  • 1989-09-28 AU AU44062/89A patent/AU4406289A/en not_active Abandoned
  • 1989-09-28 WO PCT/US1989/004258 patent/WO1990003246A1/en not_active Ceased

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