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«Immersion Silver Processing Guide FOR PRINTED CIRCUIT BOARD MANUFACTUERS PROCUT OVERVIEW Florida CirTech’s Immersion Silver process plates a silver ...»

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Product Data Sheet

Immersion Silver Processing Guide



Florida CirTech’s Immersion Silver process plates a silver coating on copper. This silver coating is used as a lead-free

solderable finish on printed circuit boards. Immersion Silver is a co-planar, dense finish that contains only silver. It is

compatible with all assembly fluxes and solder pastes.

Our Immersion Silver process consists of an acid cleaner, a peroxide-sulfuric microetch, an acidic pre-dip, the IS150 immersion silver bath, and an optional anti- tarnish bath called IS175. In the unlikely event that silver tarnish forms, we can provide a silver tarnish remover called STR199 that can be used to remove silver tarnish.

Florida CirTech’s Immersion Silver finish has a shelf life greater than 1 year, and is solderable through multiple assembly operations. Immersion silver does not migrate into copper, like immersion tin. As a result, the shelf life of immersion silver is much longer than immersion tin finishes.



•DI water must be high purity, and be free of halides (e.g. chlorides).

•If halides are drug into the IS150 bath, then silver will precipitate out, and the silver deposit quality will decrease.

Florida CirTech is a global leader in Printed Circuit Board Technology.

Visit www.floridacirtech.com for more information.

Product Data Sheet


MATERIALS (Listed in order of preference.) TANKS: Polypropylene, Polyethylene, or CPVC. Do not use PVC RACKS & BASKETS: Plastic coated stainless steel; use polypro or Halar (black or green). Do not use PVC.

HEATERS: Quartz, Enamel, Teflon, or PTFE PUMPS: Non-metallic centrifugal or magnetic-drive FILTERS AND HOUSINGS: Polypropylene, Polyethylene. Do not use PVC


1. Ventilation recommended for each chemical tank.

2. Work-bar agitation recommended for the line to aid in chemical action and rinsing.

3. Do not use air agitation in any step of this process.


PC-5012 Acid Cleaner

• Heated to 110 - 130 F.

• Circulation pump recommended, but not required.

CirEtch 130

• Heatedto75-85F.

• Ventilation is required for this bath.

Immersion Silver Pre-Dip

• A heater is recommended, but not required.

• Circulation pump with filtration required.

• Circulation rate of 3 - 5 turnovers per hour.

• Filter ratings of 20 micron.

• Ventilation is required for this bath.

IS150 Immersion Silver

• Heated to 110 - 130 F.

• Circulation pump with filtration required.

• Circulation rate of 3 - 5 turnovers per hour.

• Filter ratings of 20 micron.

• Ventilation is required for this bath.

IS175 Silver Anti-tarnish

• Heated to 90 - 110 F.

• Circulation pump recommended, but not required.

Water Rinses

• All rinses must be De-ionized water and cannot contain halides (e.g. chlorides).

• Rinse volume turnover of 2 -4 times per hour.

• The final DI water rinse is heated to 110 – 130 F, mainly to speed drying.

OPTIONAL Horizontal conveyorized equipment can be used, with immersion, flood bar agitation.

Product Data Sheet


General Comments Bath makeup must be done with reagent grade nitric acid, and DI water. Contamination of the pre-dip or silver baths with impurities like halogens (chlorides) can lead to precipitates and poor bath performance. For example, chlorides added to the silver bath will result in precipitation of the silver as silver chloride, which is a white, insoluble powder. Tap water commonly has chlorides added to it, so the use of DI water for bath makeups and rinses is critical.

The pre-dip and silver baths should be analyzed and additions made on a regular basis. The pre-dip bath contains nitric acid and organic compounds. The silver bath contains nitric acid, silver, and organic compounds.

Bath Replacement The pre-dip and immersion silver baths need to be replaced based on usage. During use, the immersion silver bath dissolves copper. When the immersion silver bath reaches 5.0 g/L of copper, both the pre-dip and the silver bath should be replaced. Furthermore, when 5 metal turnovers are reached in the silver bath, both the pre-dip and silver baths should be replaced.

Tank Preparation All process tanks should be prepared by leaching with appropriate chemicals, followed by several rinses with DI water. The leaching processes are shown below. In each case, the tank should be filled with the appropriate chemical, and then recirculation pumps turned on (if present). The dwell time for each step is at least 1 hour. If the step states 2x, then that particular item should be repeated twice, for at least 1 hour each time.

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DI Water Test It is critical that the DI water used in this process is free of halides. A simple test can determine if halides are present in the water.

Halide Test Procedure for DI Water

1. Add about 50 – 75 mL of DI water to a clean, dry beaker.

2. Add about 5 mL of 50% by vol. nitric acid, reagent grade.

3. Drop in 0.1 M silver nitrate solution, slowly while mixing.

4. If turbidity, or a precipitate forms, then halides are present in the water.

5. If the mixture stays clear, then the water is free of halides.

Product Data Sheet If halides are present in the water, then it cannot be used in this process. Contact your local water purification company for recommendations on how to remove halides. Typically this is done by using either DI (deionized) or RO (reverse osmosis) purified water.

DI water rinses should be run at flow rates of 2 - 4 volume turnovers per hour to ensure adequate rinsing.

Bath Makeup The makeup quantities are shown below for both the Pre-dip and Silver baths. Follow the order given in the table for additions, and mix well after each step.

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* It is critical that the water be free of halides. See the test above.

All analysis procedures are detailed in section V. below. A summary of the control ranges for each bath are shown in the table below.

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*Analytical procedures and control ranges can be found in the Technical Bulletins for each product.

Reagent Information The following reagents are required for the IS150B titration. They can be purchased from Sigma-Aldrich at 1The catalog number information is shown below.

Hexamethylenetetramine solution [CAS# 100-97-0] Makeup: 20% by weight dissolved in DI water Sigma-Aldrich Catalog #: H11300-500G Chromeazurol S indicator [CAS# 1667-99-8] Makeup: 0.1% by weight dissolved in DI water Sigma-Aldrich Catalog #: 199532-25G Copper (II) nitrate hydrate [CAS# 19004-19-4] - 0.01 M Makeup: Dissolve 2.32 grams into 1 liter of 2% by vol. nitric acid Sigma-Aldrich Catalog #: 467855-50G


PC-5012 Acid Cleaner Copper cleaning action and drag out reduces the concentration of PC-5012. Weekly analysis and addition of PC-5012 concentrate is recommended.

CirEtch 130 Microetch rate is controlled by Cir130A concentration. We recommend an etch depth of 10-30 microinches.

Sulfuric acid concentration controls the solubility of copper in solution. Cir130W can be added in small amounts to control misting. Bath analysis and additions of sulfuric acid and Cir130A should be performed daily.

Pre-Dip for Immersion Silver As the pre-dip is used, the acid normality and IS150B concentrations drop. Additions of nitric acid and IS150B will keep the bath in specifications. Analysis should be performed weekly. Over time, the pre-dip can form a precipitate, which needs to be removed by filtration. The precipitate does not affect bath performance, and is normal. The pre-dip should be discarded and remade when the copper content of the Immersion Silver bath reaches the high limit, as detailed below.

Product Data Sheet IS150 Immersion Silver As the Immersion Silver bath is used; silver, acid normality and IS150B content all drop, and copper content increases. Copper is dissolved as silver is plated. Additions of nitric acid, IS150A and IS150B will keep the bath in specifications. Analysis of the IS150 Immersion Silver bath and additions should be performed daily.

When the copper level reaches 5000 ppm (5 g/L), then the Immersion Silver bath should be replaced. The pre-dip should also be replaced at the same time. Over time, the IS150 Immersion Silver bath can form a precipitate, which needs to be removed by filtration. The precipitate does not affect bath performance, and is normal.

IS175 Anti-tarnish Anti-tarnish is consumed as the silver is coated with this protective chemical. There is no analysis for the active ingredient. This bath should be dumped and remade when approximately 600 square feet of circuit board area has been processed per gallon. The bath should also be remade if performance decreases.


The immersion silver coating is comprised of pure silver over copper. We recommend maintaining the pure silver layer thickness between 5 and 30 microinches to ensure good solderability through multiple assembly cycles.

Silver thickness is best measured by XRF. We recommend the use of a collimator with a diameter that is at least 3x smaller in size than the feature that is being measured. Silver thicknesses on large pads can be much lower than on smaller pads. We recommend taking readings on various pad sizes, and using an average value for the measurement.



• Immersion silver coated boards should be rinsed and dried thoroughly. They should be packaged in sulfur free plastic bags as soon as possible after coating.

• Wear gloves when handling silver plated PWBs. Fingerprints can cause tarnish and solderability issues.

• Store PWBs at room temperature in clean and dry areas. Contaminates and high temperatures will degrade the silver surface.

• Electrical testing after Immersion Silver processing is preferred.

• If PWBs are washed after routing, it should be done with clean DI water. Make sure that the PWBs are dried well after washing.


It is the nature of silver to tarnish, which appears as a yellow to yellow-brown color. Tarnish can be minimized or prevented by taking certain precautions. These precautions are detailed below.

• Follow the general handling guidelines above.

• Ensure that the rinses following the IS150 Immersion Silver bath are filled with clean DI water.

• Dry the PWBs promptly and completely after immersion silver plating, using a clean dryer.

• Store the PWBs in a clean and dry environment.

• Sulfur compounds will cause silver tarnish. Ensure that sulfur containing compounds do not come into contact with the PWBs.

STORAGE Product Data Sheet It is good practice to store silver plated PWBs as soon as possible after plating. Store silver plated PWBs interleafed with paper, and inside plastic bags. The bags and paper must be sulfur free. Do not use rubber bands. Contaminates in the rubber can cause markings and tarnish on the silver, even through plastic bags.

Silver plated PWBs should be stored at room temperature and humidity.


In the event that tarnish forms on the silver surface, tarnish can be removed by using our STR199 Silver Tarnish Remover. Contact your Florida CirTech representative for details. The process steps for STR199 are shown below.

Silver Tarnish Removal

1. Immerse the boards in STR199 solution.

(Read the STR199 technical bulletin for details)

2. Rinse several times using clean DI water

3. Dry completely.

4. Protect the silver coating using IS175 Silver Antitarnish.

It is possible to completely strip and re-plate the silver finish, if necessary. During silver stripping, cosmetic defects can form in the copper which are later translated into the re-plated silver deposit. It is very difficult to clean the copper sufficiently to remove these cosmetic defects. If silver stripping is necessary, then use the following process.

Silver Stripping (Permanganate)

1. Immerse the boards in a working permanganate desmear type bath, until the silver is completely removed.

An addition of about 5 – 10% by volume of ammonium hydroxide solution will speed stripping and brighten the copper surface.

2. Rinse several times.

3. Immerse in a working neutralizer bath.

4. Rinse several times.

5. Microetch about 40 – 60 microinches of copper. More may be required to clean the surface.

6. Rinse several times.

7. Run through an aluminum oxide jet scrub to buff the copper surfaces.

8. Run the boards through the complete immersion silver process to recoat with silver.

An alternate silver stripping procedure is shown below.

Silver Stripping (Alternate)

1. Run the tarnished silver boards through HASL to coat with solder.

2. Strip the solder using a standard tin/solder strip chemistry.

3. Clean the copper by microetching 40–60 microinches.

4. Run through an aluminum oxide jet scrub to buff the copper surfaces.

5. Run the boards through the complete immersion silver process to recoat with silver.


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