Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/22—Secondary treatment of printed circuits
  • H05K3/24—Reinforcing the conductive pattern
  • H05K3/244—Finish plating of conductors, especially of copper conductors, e.g. for pads or lands
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/30—Electroplating: Baths therefor from solutions of tin
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/30—Electroplating: Baths therefor from solutions of tin
  • C25D3/32—Electroplating: Baths therefor from solutions of tin characterised by the organic bath constituents used
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/48—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor
  • H01L23/488—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor consisting of soldered or bonded constructions
  • H01L23/495—Lead-frames or other flat leads
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/22—Secondary treatment of printed circuits
  • H05K3/24—Reinforcing the conductive pattern
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
  • H05K2201/07—Electric details
  • H05K2201/0753—Insulation
  • H05K2201/0769—Anti metal-migration, e.g. avoiding tin whisker growth
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/22—Secondary treatment of printed circuits
  • H05K3/28—Applying non-metallic protective coatings
  • H05K3/282—Applying non-metallic protective coatings for inhibiting the corrosion of the circuit, e.g. for preserving the solderability

Definitions

• the present invention relates to a method for depositing tin in a manner to reduce, minimize or prevent tin whisker growth from such deposits, as well as to electroplated components formed by such a method. More particularly, the invention relates to a modification or treatment of the deposit to render it less prone to whisker growth. In particular, prevention of oxide formation and/or corrosion reactions on the tin deposit surface or post treatment of the deposit surface has been found to be effective for this purpose.
• tin or tin alloy electroplated deposit has become increasingly important in fabricating electronic circuits, electronic devices and electrical connectors because of the benefits that such deposits provide.
• tin and tin alloy deposits protect the components from corrosion, provide a chemically stable surface for soldering and maintain good surface electrical contact.
• tin and tin alloy deposits protect the components from corrosion, provide a chemically stable surface for soldering and maintain good surface electrical contact.
• tin and tin alloy deposits protect the components from corrosion, provide a chemically stable surface for soldering and maintain good surface electrical contact.
• tin and tin alloy deposits protect the components from corrosion, provide a chemically stable surface for soldering and maintain good surface electrical contact.
• tin or tin alloy deposits protect the components from corrosion, provide a chemically stable surface for soldering and maintain good surface electrical contact.
• Such deposits are typically produced by electroless plating or electroplating. Regardless of the deposition process employed, it is desirable to form smooth and level deposits of tin on the substrate
• tin whiskers When pure tin is used and is applied to a copper or copper alloy substrate, the resulting deposit suffers from interdif fusion of base material copper into the tin deposit and subsequent formation of copper-tin intermetallic compounds. While these copper-tin compounds can be brittle and may impair the usefulness of the tin coated component, their presence also results in compressive stress formation in the tin deposit. Subsequently, the generation of metal filaments known as tin whiskers sometimes grow spontaneously from these tin deposits. These whiskers are hair-like projections extending from the surface and may be either straight or curled or bent. Tin whiskers typically have a diameter of about 6 nanometers to 6 microns. The presence of such whiskers is undesirable due to the very fine line definition required for modern circuitry, since these whiskers can form both electrical shorts and electrical bridges across insulation spaces between conductors. The whiskers may create shorts or introduce failures into electronic circuitry.
• Another approach is to treat the surface of the substrate before applying the tin deposit.
• Ultrasonic agitation of the plating solution and/or alternating the polarity of the electrodes during plating have been suggested to reduce the amount of hydrogen absorbed or occluded in the structure of the plating metal.
• whisker inhibiting element addition to the tin plating solution.
• the most common approach has been to deposit an alloy of tin and lead. This alloy is also compatible with the solders that are later used to make electrical connections to wires or other electrical components.
• lead and a number of other alloying elements are undesirable due to their toxicity and related environmental issues.
• pure tin or very high tin content deposits are now used, and these are subject to whiskering under certain conditions. This is particularly significant problem for small electronic parts that are provided with a tin deposit, as short circuits can result.
• tin when exposed to heat & humidity converts to tin oxide which in turn can result in localized compressive stress (due to localized volume increase) and/or a corrosion reaction due to water condensation in association with exposed base material forming a galvanic couple which induces compressive stress which becomes the driving force for tin whisker growth, as shown in the diagrams of the Dittes article.
• the invention relates to a number of methods for reducing tin whisker formation or growth in tin deposits on a substrate.
• at least one physical property or characteristic of a tin deposit is modified during deposition of the same on a substrate or immediately thereafter.
• the tin deposit is provided on the substrate with at least one physical property or characteristic that renders it less prone to tin whisker formation or growth so that tin whiskering is substantially reduced or is even prevented.
• the tin deposit can be provided on the substrate as a fine grain structure which minimizes tin whiskering, where the tin deposit preferably has an average grain size of about 0.05 to 5 and preferably less than about 2 to 3 microns.
• the tin deposit can be treated during deposition to render it less prone to tin whisker formation or growth. This can be done by rendering the tin deposit essentially free of surface oxides to minimize tin whiskering thereon.
• the prevention of surface oxide formation is conveniently achieved by providing the tin deposit from a solution containing a phosphorous compound, thereby incorporating trace or small amounts of phosphorous in the tin deposit.
• the tin plating solution contains sufficient phosphorous compound to provide an amount of about 0.1 ppm to 30% by weight phosphorus in the tin deposit.
• the tin deposit is treated after deposition to render it less prone to tin whisker formation or growth.
• a protective coating upon the tin deposit (i.e., after the tin plating is completed).
• the tin deposit can be immersed in or contacted by a post-treatment solution containing one or more of a phosphorous compound, an organic compound, a mercaptan, or an organo-metallic compound.
• the protective coating is applied at a thickness of about 0.1 angstroms to 1 micron.
• the invention also relates to an improvement in a tin plated electronic component that includes a copper surface upon which a fine grained tin deposit is present.
• the improvement comprises minimizing or preventing tin whisker formation or growth by providing the tin deposit with one or more of (a) a fine grained structure so that the tin deposit is less prone to tin whisker formation or growth compared to tin deposits having larger grain structures; (b) trace or small amounts of phosphorous so that the tin deposit is essentially free of surface oxidation and is less prone to tin whisker formation or growth compared to tin deposits having surface oxidation; or (c) a protective layer so that it is less prone to tin whisker formation or growth compared to tin deposits having no protective layer.
• the present invention relates to creating a tin deposit which is inherently less prone to oxide formation and/or corrosion reactions on the tin deposit surface through use of one or more methods for reducing whisker formation in tin deposits on a substrate.
• One method comprises creating a tin deposit which is inherently less prone to oxide formation and/or corrosion reactions on the tin deposit surface through use of: (i) the deposition of a "finegrained" tin deposit with an average grain diameter in the range of 0.05 to 5 microns, such a grain diameter resulting in a tin deposit which is inherently less prone to surface oxidation; (ii) the use of a phosphorous compound in a solution that is used to deposit the tin deposit on a substrate which thereby incorporates trace amounts of phosphorous in the tin deposit which in turn reduces tin oxide formation on the surface during exposure to heat and/or humidity; and/or (iii) the use of a phosphorous compound, organic, mercaptan,
• the invention also relates to a plated substrate that includes a tin deposit with reduced surface oxidation and/or corrosion characteristics in the layer comprising tin.
• the layer comprising tin preferably includes no less than 80% tin by weight and preferably much higher amounts of tin without experiencing significant whiskering. Even deposits of essentially pure tin (i.e., tin with no intentionally added alloying elements and which contains no other elements except for incidental impurities) can be deposited without experiencing significant whiskering problems.
• the substrate can be an electronic component that includes non- electroplatable portions and electroplatable portions which are to be plated.
• the tin content of the deposit is greater than 80% to 100% by weight of the deposit.
• alloying elements can be added to the solution used to deposit tin to provide a deposit of a tin alloy.
• the tin plating solutions that are useful in the present invention include, but are not limited to those described below:
• Tin fluoborate plating baths are widely used for plating all types of metal substrates including both copper and iron. See for example, U.S. Patent Nos. 5,431 ,805, 4,029,556 and 3,770,599. These baths are preferred where plating speed is important and the fluoborate salts are very soluble.
• HALIDE SOLUTIONS Tin plating baths with the main electrolyte being a halide ion (Br, Cl, F, I) have been used for many decades. See for example, U.S. Patent Nos. 5,628,893 and 5,538,617. The primary halide ions in these baths have been chloride and fluoride.
• SULFATE SOLUTIONS Tin and tin alloys are commercially plated from solutions with sulfate as the primary anion. See for example U.S. Patent Nos. 4,347,107, 4,331,518 and 3,616,306.
• Patent Nos. 6,132,348, 4,701,244 and 4,459,185 The cost of the alkyl sulfonic acid is relatively high, so that the preferred sulfonic acid used has been methane sulfonic acid (MSA) although the prior art includes examples of other alkyl and alkanol sulfonic acids.
• MSA methane sulfonic acid
• the performance advantages of alkyl sulfonic acid baths include low corrosivity, high solubility of salts, good conductivity, good oxidative stability of tin salts and complete biodegradability.
• the amount of tin (as tin metal) in the plating solutions of the present invention may be varied over a wide range such as from about 1 to about 120 grams of metal per liter of solution (g/1), or up to the solubility limit of the particular tin salt in the particular solution. It should be understood that the foregoing quantities of tin in the plating solution are disclosed as metallic tin, but that the tin may be added to the solutions in the form of tin compounds. Such compounds may include, for example, tin oxide, tin salts, or other soluble tin compounds, including formates, acetates, sulfates, alkane sulfonates, hydrochlorides and other halides, carbonates and the like.
• surfactant and wetting agents can be used as desired.
• the surfactants are selected to achieve the desired deposit qualities and characteristics.
• the examples illustrate commercially available baths that include preferred surfactants and/or wetting agents to provide the desired tin deposits according to the invention. Any of the surfactants mentioned in US patent 6,860,981 can be used, so that patent is incorporated herein by reference thereto for its disclosure of such components.
• any of the generally tin or tin-lead surfactants known in the prior art can all be used but when a fine grained deposit is desired, a secondary grain refiner is generally used in combination with the surfactant(s).
• alloying elements can be added to the tin plating solution. These are primarily added in an amount such that less than 5% of the alloying element is present in the deposit. Preferred alloying elements include silver (up to 3.5% of the deposit), bismuth (up to 3 % of the deposit), copper (up to 3% of the deposit) and zinc (up to 2% of the deposit). While other alloying elements can be used, it is generally not preferred to use those that may have an adverse effect on the environment, i.e., antimony, cadmium, and particularly lead. Preferably, as noted above, alloying elements are optional, and the tin content of the deposit is as high as possible, usually on the order of as high as 99% by weight or more with the balance being unavoidable impurities.
• tin whisker growth is prevented or at least substantially minimized by depositing a fine-grained tin deposit with an average grain diameter of 0.05 to 5 microns.
• a more preferred grain diameter is 1 to 3 microns.
• Any tin electroplating solution which can create an average grain diameter in the aforementioned range can be used but as noted above those described in US Patent No. 6,860,981 are preferred.
• a secondary grain refiner is used to assure that a fine grain structure is obtained in the deposit.
• the additives biquinoline and dimethyl-phenanthroline in particular are preferred secondary grain refiners which reduce the grain size although other materials known by those skilled in the art could also be used to achieve the same result.
• the desired grain size In order to confirm that the desired grain size is achieved, it is conventionally measured with a scanning electron microscope (SEM) at 2000X and 5000X magnification, with a photo taken that has a scale on it to measure the grain diameter of multiple grains of the tin deposit. An average of the measurements is taken to determine grain size.
• SEM scanning electron microscope
• What differentiates the present invention from the prior art is the fact that SEM measurement is used to confirm that the grain size is within the desired range. While it may be possible that this type of fine grain structure can occur in some of the prior art baths, that would occur purely by coincidence and in an unintentional manner. In this invention, the presence of the fine grained structure is confirmed to obtain the desired reduction or elimination of tin whiskering.
• Tin deposits of varying grain sizes were exposed to high heat & humidity conditions to purposely enhance tin oxide formation and these were subsequently analyzed by Surface Electrochemical Reduction Analysis ("SERA").
• SERA Surface Electrochemical Reduction Analysis
• the fine-grained tin deposits (average grain diameter 0.05 to 3 microns) consistently produced lower thickness of tin oxide on the surface compared to the conventional, larger grain diameter tin deposits (average grain diameter of above 3 to 8 microns).
• this phenomenon is due to the fact that the finegrained tin deposits have a generally smoother surface structure and therefore less exposed microscopic "peaks” and “valleys” compared to the large generally coarse-grained tin deposits and this leads to a smaller exposed surface area for oxidation/corrosion reactions to occur on the fine grained tin deposits compared to the large grained tin deposits. It is also believed that the multiple grain boundaries of the fine grained structure act as a stress distribution or stress relieving network to prevent compressive stress on the deposit from concentrating and then generating tin whiskers.
• a phosphorous compound in a solution that is used to deposit the tin deposit on a substrate which thereby incorporates trace amounts of phosphorous in the tin deposit in turn reduces tin oxide formation on the surface during exposure to heat and/or humidity.
• Preferred solutions and amounts of phosphorus to add are disclosed by Zhang et al. in US Patent 6,982,030, a patent which discusses the use of such additives in the context of improving deposit solderability.
• the method originally disclosed in that patent can be used to provide benefits in minimizing tin whisker growth as well as in the reduction of surface oxidation when deposits are provided under the conditions previously described in that patent.
• the use of one or more of a phosphorous compound, organic, and/or organo-metallic compound in a solution is used to apply a protective coating to the surface of a previously electroplated tin deposit, with the protective coating acting to minimize or prevent oxide formation and/or corrosion of the tin deposit during exposure to heat and/or humidity.
• Tarniban, Tarniban 51, Tarniban E260 all available from Technic, Inc., Cranston, RI, are examples of solutions that contain such additives; additionally the examples section that follows identifies other useful specific compounds for this purpose.
• This "post-treatment" process applies a thin film (0.5 angstroms to 0.5 microns thickness) to the tin deposit surface which effectively blocks and thereby minimizes negative reactions from occurring such as oxidation and/or corrosion, both of which are now known to be the driving force for tin whiskers during high heat and humidity exposure.
• EXAMPLE 1 (Comparative): Tin was electroplated from an MSA electrolyte ("Solderon ST300" from Rohm & Haas) onto a Cu alloy substrate (Cu99.85%, SnO.15%) at a current density of 150 A/ft 2 for a period of time sufficient to obtain an average of lO ⁇ m tin deposit thickness. The grain size of the tin deposit was measured and found to be 5-8 microns average grain diameter. The deposit was subjected to high temperature and humidity (HTH) testing of 155 deg C for 16 hrs (in an uncontrolled humidity environment) followed by 97 deg C / 99% relative humidity (RH) conditions for 8 hrs.
• HTH high temperature and humidity
• This deposit was measured by SERA and the tin oxide thickness on the surface was found to be 122 angstroms.
• This deposit was subjected to the high temperature & humidity whisker test condition specified by JEDEC STANDARD JESD22A121 "Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes", specifically: high temperature/humidity storage of 60°C/90% RH for 3000 hrs.
• the maximum whisker length was measured and was determined to be 112 ⁇ m.
• EXAMPLE 2 Tin was electroplated from a mixed acid sulfate electrolyte ("Technistan EP" from Technic Inc) onto a Cu alloy substrate (Cu99.85%, SnO.15%) at a current density of 150 A/ft 2 for a period of time sufficient to obtain an average of lO ⁇ m tin deposit thickness.
• the grain size of the tin deposit was measured and found to be 1-2 microns avg. grain diameter.
• the deposit was subjected to high temperature & humidity (HTH) testing of 155 deg C for 16 hrs (in an uncontrolled humidity environment) followed by 91 deg C / 99% relative humidity (RH) conditions for 8 hrs.
• HTH high temperature & humidity
• This deposit was measured by SERA and the tin oxide thickness on the surface was found to be 68 angstroms.
• This deposit was subjected to the high heat & humidity whisker test condition specified by JEDEC STANDARD JESD22A121 "Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes", specifically: high temperature/humidity storage of 60°C/90% RH for 3000 hrs. Upon completion of the whisker test method, the maximum whisker length was measured and was determined to be 55 ⁇ m.
• EXAMPLE 3 Tin was electroplated from a mixed acid sulfate electrolyte ("Technistan EP" from Technic Inc. which also contained a phosphorous compound at a concentration of 4 g/1 in the plating solution as described in US Patent Application No. 2004/0099340 Al) onto a Cu alloy substrate (Cu99.85%, SnO.15%) at a current density of 150 A/ft 2 for a period of time sufficient to obtain an average of lO ⁇ m tin deposit thickness. The grain size of the tin deposit was measured and found to be 1-2 microns avg. grain diameter.
• the deposit was subjected to high temperature & humidity (HTH) testing of 155 deg C for 16 hrs (in an uncontrolled humidity environment) followed by 97 deg C / 99% relative humidity (RH) conditions for 8 hrs.
• HTH high temperature & humidity
• RH relative humidity
• This deposit was measured by SERA and the tin oxide thickness on the surface was found to be 43 angstroms.
• This deposit was subjected to the high heat & humidity whisker test condition specified by JEDEC STANDARD JESD22A121 "Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes", specifically: high temperature/humidity storage of 60°C/90% RH for 3000 hrs.
• the maximum whisker length was measured and was determined to be 43 ⁇ m.
• EX AMPU 4 Tin was electroplated from a mixed acid sulfate electrolyte ("Technistan EP" from Technic Inc. which also contained a phosphorous compound at a concentration of 4 g/1 in the plating solution as described in US Patent Application No. 2004/0099340 Al) onto a Cu alloy substrate (Cu99.85%, SnO.15%) at a current density of 150 A/ft 2 for a period of time sufficient to obtain an average of lO ⁇ m tin deposit thickness. After tin plating the substrate was placed into a solution containing a phosphorous compound (phosphoric acid @ 70 ml/1) + sodium gluconate at 50 g/1.
• a mixed acid sulfate electrolyte (Technistan EP" from Technic Inc. which also contained a phosphorous compound at a concentration of 4 g/1 in the plating solution as described in US Patent Application No. 2004/0099340 Al) onto a Cu alloy substrate (Cu99.85%, SnO.15%)
• the grain size of the tin deposit was measured and found to be 1- 2 microns avg. grain diameter.
• the deposit was subjected to high temperature & humidity (HTH) testing of 155 deg C for 16 hrs (in an uncontrolled humidity environment) followed by 97 deg C / 99% relative humidity (RH) conditions for 8 hrs.
• HTH high temperature & humidity
• RH relative humidity
• This deposit was measured by SERA and the tin oxide thickness on the surface was found to be 35 angstroms.
• This deposit was subjected to the high heat & humidity whisker test condition specified by JEDEC STANDARD JESD22A121 "Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes", specifically: high temperature/humidity storage of 60°C/90% RH for 3000 hrs.
• the maximum whisker length was measured and was determined to be 38 ⁇ m.
• EXAMPLE 5 Tin was electroplated from a mixed acid sulfate electrolyte ("Technistan EP" from Technic Inc.) onto a Cu alloy substrate (Cu99.85%, SnO.15%) at a current density of 150 A/ft 2 for a period of time sufficient to obtain an average of lO ⁇ m tin deposit thickness. After tin plating the substrate was placed into a solution containing 10 ml/1 solvent (butyl cellosolve), 10 ml/1 surfactant (Jeffox WL 4000), and 4 g/1 mercaptopropionic acid at 40 deg C for 30 sec. The grain size of the tin deposit was measured and found to be 1-2 microns avg. grain diameter.
• Example 1 shows the results from a standard large-grained tin deposit which is commonly used in the industry and it demonstrates that (i) tin oxide formation is very high after heat & humidity exposure at 122 angstroms and (ii) the corresponding tin whisker growth following the JEDEC procedures is excessive at 122 microns; although no industry standard exists yet with regard to maximum acceptable whisker length it is commonly considered to be 50 microns.
• Example 2 shows the results from the current invention comprising a fine-grained tin deposit which demonstrates that (i) tin oxide formation is significantly reduced vs. the conventional large grained deposit from example 1 above after heat & humidity exposure at 68 angstroms and (ii) the corresponding tin whisker growth following the JEDEC procedures is significantly reduced vs. the conventional large grained deposit from example 1 at 55 microns, evidence that the corrosion/oxidation protection enhancement effect of the current invention is extremely effective in its ability to minimize tin whisker growth.
• Example 3 shows the results from the current invention comprising a fine-grained tin deposit combined with the phosphorous-containing additive in the tin plating solution which demonstrates that (i) tin oxide formation is significantly reduced vs. the conventional large grained deposit from example 1 and further reduced vs. the deposit in example 2 above after heat & humidity exposure at 43 angstroms and (ii) the corresponding tin whisker growth following the JEDEC procedures is significantly reduced at 43 microns, evidence that the corrosion/oxidation protection enhancement effect of the current invention is extremely effective in its ability to minimize tin whisker growth..
• Example 4 shows the results from the current invention comprising a fine-grained tin deposit combined with the phosphorous-containing post-treatment solution which demonstrates that (i) tin oxide formation is significantly reduced vs. the conventional large grained deposit from example 1 and further reduced vs. the deposit in Examples 2 & 3 above after heat & humidity exposure at 35 angstroms and (ii) the corresponding tin whisker growth following the JEDEC procedures is significantly reduced at 38 microns, evidence that the corrosion/oxidation protection enhancement effect of the current invention is extremely effective in its ability to minimize tin whisker growth.
• Example 5 shows the results from the current invention comprising a fine-grained tin deposit combined with the organic-containing post-treatment solution which demonstrates that the corresponding tin whisker growth following the JEDEC procedures is significantly reduced at 33 microns, evidence that the corrosion/oxidation protection enhancement effect of the current invention is extremely effective in its ability to minimize tin whisker growth.

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• 2006
  • 2006-06-23 CN CNA2006800296042A patent/CN101243210A/zh active Pending
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