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October 16, 2018

Silver Solder for Audio Circuits

We manufacture an audio product. We have been told to use silver solder for all solder connections. Can silver solder possibly have any impact on the quality of our product, or will standard, lower-cost eutectic solders work just as well?


Expert Panel Responses

Comparedto conventional tin& lead alloys, a much greater corrosion favoring effectexists with silver-based solders due to the high solubility rate of silverhydroxide in moisture films and the low critical relative humidity of 60%. Inparticular, carboxylic acid-based activators in solder pastes can result in asteady increase of the adsorbed moisture film. It is therefore possible thatthe value of the critical humidity level could drop below levels that aretypically found in air-conditioned rooms. The removal of hygroscopic residues(carboxylic acid, salts) through assembly cleaning can contribute to asignificant improvement of resistance to elevated humidity levels and reducesusceptibility to migration. The phenomenon can be explained by the uniformdistribution of the silver with a maximum of 4% in the soldered joint. Theelectro-chemical migration mechanism activates only the silver that is close tothe surface of the soldered joint. This means that only low concentrations ofsilver hydroxides are available. Accordingly, only filigree dendrites with avery low current-carrying capacity can be formed. These dendrites lower thesurface resistance primarily in the final stage of their growth, but are thenburnt off by a short-circuit effect so that the original surface resistance isre-established. At normal (ambient) temperatures, the rate of renewed silver supply tothe surface of the solder joint is slower than the attack by electrochemicalmigration. This is the reason why short-life bridges are repeatedly formed thathave never transformed into constant short-circuits. This phenomenon results ininexplicable defect patterns in electronic assemblies that cannot besystematically repeated and not be discovered by discontinuous resistancemeasurements.

Umut Tosun
Application Technology Manager
Zestron America
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".

Allelements of the conductive path for audio signals have the potential for adding"noise" (aka: hiss, buzz, hum, etc) to the audio signal. Resistors are one ofthe most common sources of noise in audio circuits, carbon film being one ofthe worse, so most will use a lower noise generating resistors such as: metalfile, wire wound, carbon comp, or foil type resistors, each having a trade-offbetween noise generation, size, and cost. It stands to reasonthat solder joints can also add noise, since the audio signal may pass throughhundreds of solder joints on its way to your ears. Audio "purists" recommend asilver alloy solder, usually around 4% Ag. The use of a silver solder in audioequipment can be one the many hidden differences between lower priced audioproducts and "high end" professional audio equipment.

Paul Austen
Senior Project Engineer
Electronic Controls Design Inc
Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 39 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes and well as moisture sensitive component storage solutions.

I would venture to sayfollowing.
  1. If you are an OEMthen I don't see that Silver solder is going to make that much of a difference.
  2. If your product ishigh end & directed to professional usage or to audiophiles (sic) then it'sa selling point for your brochure.
  3. If you are a subcontract assembler & your customer is asking for silver solder, then use it& pass along the costs related
  4. Experience &research tells me that it makes little or no difference in audible -- &that's the issue -- quality.How many millions of car radios are out there?Silver solder? I don't think so.

Jerry Karp
JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.

What is the composition of the silver solder? What are the reliability requirements? There are lower-temp eutectic alloys (cheaper or more expensive) that can be used based on the reliability requirements, solder process, equipment used.

Karthik Vijay
Technical Manager - Europe
Indium Corp.
Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.

I agree with Jerry K's points (2) and (3). In addition,let me offer some insight into what may be driving the advice to use asilver-bearing solder. Silver is the best-available electrical conductor, andhas a long history in electronics. Audiophiles are a notoriously superstitiousbunch, and have shown a shocking tendency to believe technical claims that havenot been demonstrated to have an *audible* effect on equipment performance. So, can a silver solder really improve the sound of theresulting equipment? Perhaps, but I am somewhat dubious. We could talk all dayabout skin effects, thermal (Johnson-Nyquist) noise, etc., but the bottom lineis, if there is an audible effect, it should show up as detectable signaldegradation at the frequencies of interest. The whole question may be somewhat moot, however. If theassemblies you are producing are Pb-free, then it's easy to select a Sn-Ag-Cusolder that contains approx. 4% Ag. The cost difference between that andlower-Ag alloys is not that great.

Fritz Byle
Process Engineer
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.