Ask the Experts
March 3, 2023 - Updated
September 24, 2020 - Originally Posted

Challenge Wetting Solder to Brass Pins

In our production we have a product with a connector. The connector pins are made of brass, and tin plated. Unfortunately, the connector pin plating is made by the supplier before cutting and forming the connector pins, so some part of the pins remain unplated, leaving exposed brass.

In our selective soldering process, we have difficulty getting solder to wet to the brass exposed part of the pins. Any recommendations to solve the issue, apart from changing the connector with ones which is more wettable?


Expert Panel Responses

In order to give a good answer, it would be necessary to know more about your product (IPC Class 1, 2, or 3), the connector lead-form, and the process you intend to use.

Generally speaking, it would not be a good idea to continue trying to solder a component with incomplete or inconsistent tin plating. If the plating bond is as weak as you described, solder joint reliability will be very poor.

I would recommend that you either work with the component supplier to improve their plating process or select a different component with plating that is compatible with your intended process.

Rick Kompelien
Principal Product Engineer
Benchmark Electronics, Inc.
30+ years of experience working with electronic and electro-mechanical manufacturing and design (medical, automotive, military, computer, and industrial controls). Military veteran - served as a Combat Engineer with the United States Marine Corps.

You could run the leads through a tinning operation prior to through-hole soldering. This would cover the brass with solder and make it "solderable" for subsequent through-hole soldering.

Alternatively you could use a high activity flux that will enable soldering to exposed brass. Most water soluble liquid fluxes are high activity, and some will work with oxidized copper and brass surfaces.

I suggest contacting your flux supplier for specific recommendations.

Tony Lentz
Field Applications
FCT Assembly
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.

Have you tried superior 75 flux? If not, this might be the solution. Following the manufacturer guidelines is strongly recommended.

David Cormier
Engineering Manager
Circuit Technology Center, Inc.
Manufacturing Engineer of 20+ years. Involved in Industries relating to all sectors of defense, Commercial product Industries, RF - Microwave and Semiconductor industries. Vast knowledge and experience relating Mil-STD’s, IPC-STD’s, EAI-STD’s, GEIA-STD’s, J-STD’s and MIL-PRF-STD’s.

Soldering to Brass is almost impossible in the electronic assembly manufacturing. Brass consist of Copper and Zinc a mixture or alloy which is rare in electronic assemblies.

My suggestion would be to retin the brass with tin prior to assembly to any electronic assembly.

The suggested flux would be a Zinc Chloride plumbers flux as this would prepare the brass to be tin by the solder alloy. Dip the parts into a solder pot and tin the leads which will be soldered by the selective soldering process. Follow this tinning process with a high performance cleaning process as the flux must be completely removed. At this point the lead would be more solderable and would be easier to solder.

I would also check the solderability of the lead to verify the goodness of the tinning process.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Brass pins of the connector solder not happen because of brass pins has contamination with moisture that Soldering wetting not Happened or it may be partially solder. Suggestion: to the Rh factor Humidity level between 35 to 60% and Shop floor temp 22 to 27 deg. Celsius.

Raju Wagh
Senior Engineer SMT
Advance Power Display system Ltd Mumbai
Mr. Raju Wagh has worked in the electronics industries for the past 20 years focused in TV manufacturing, mother boards, mobile, LED lighting, power supply manufacturing and more. His specialty is in SMT production and processes

I cannot find a requirement that the tip of the lead be covered in solder in IPC-A-610, as long as the barrel fill and fillet requirements are met. In fact, Section give the acceptability requirements for Lead Cutting After Soldering, which would expose the base metal. Section 8.3.13 on Bottom Termination Components (QFNs) shows where wetting will not occur in an exposed base metal condition.

Pre-tinning the leads with a more aggressive flux such as an OA Water Soluble or using such as flux in the selective solder process are about the only alternatives. Be sure that the assemblies are properly cleaned if you use the more aggressive flux chemistry.

Kevin Mobley
PCBA Engineering Liaison
General Atomics Electromagnetic Systems Group
Kevin has over 30 years of experience in process and manufacturing engineering serving in both EMS and OEM companies. Expertise includes all aspects of SMT as well as wave solder and CCA materials such as PCBs, solder material, and component finishes. Kevin has developed processes for thousands of assemblies from stencil printing to conformal coating and testing.

Brass in normal conditions is very difficult to solder and wet because is a material very sensitive to oxidation. In selective soldering process this issue is hard to fix because typically the fluxes are zero or low halides whit less activity in order to no have reliability issues.

There are some alternatives to solder component lead with exposed brass, however implicate change flux or additional steps on your process and analysis.

Apply more flux. Apply more flux probably helps to increase the solids deposit on the lead and helps to improve the wetting. ( be careful to not exceed the solids deposit of flux recommended by supplier or splash out flux in areas that don't needed).

Change flux type, You can use a more active flux or more solids. ( This solution implicate validations and contaminations test). In selective solder low or zero halides flux are recommended to avoid reliability issues).

Pre-tin process. before assembly your component, you can pre-tin the component lead with a mini solder pot. This is not the best solution but can works as a containment action.

The best solution is request changes to your supplier that fix this issue considering that the soldering process will be selective solder.

Andres Rojas
Engineering Director / Master IPC Trainer (MIT)
AMMSA Solutions
More than 20 years of technical experience in the electronics industry in roles ranging from Process & Project Engineer to engineering manager and Technical Applications Engineer for Latin Americas. IPC Master Trainer, International speaker and consultant.

There are several areas that you should investigate:
  1. Is the flux your are using active enough to remove the oxides present on the exposed metal pins?
  2. Is your nitrogen source at a low enough ppm level (1000 ppm or lower at the soldering point) that it is providing you with the proper soldering environment?
  3. You can investigate using forming gas blends (4 to 5% H2 in remainder N2); this can assist in removing metal oxides.

Gregory Arslanian
Global Segment Manager
Air Products & Chemicals, Inc.
Mr. Arslanian has been involved in electronics packaging processing and equipment since 1981 including flipchip, TAB, wirebonding and die attach. Current responsiblities include R&D, applications, marketing and customer interaction.

In general brass is a difficult base metal to solder since it is an alloy of copper and zinc, with zinc being very difficult to solder. Without knowing more details about what flux you’re using you could use a more aggressive flux but this could present issues with your selective soldering equipment in terms of corrosion of the fluxer and other parts of your machine. A better alternative would be to have the connector pins stripped of the tin plating and re-tinned by an outside component processing house using organic acid flux followed by application of lead-free or tin-lead plating with the aggressive organic acid flux being cleaned off before your in-house selective soldering process.

Carlos Bouras
General Manager
Nordson SELECT
Carlos Bouras is the General Manager of Nordson SELECT and has over 30 years of experience in the electronics manufacturing industry. Carlos's expertise is in process engineering, product development and manufacturing operations. For the past 15 years Carlos has focused specifically on automated assembly issues and is the holder of several US patents for non-contact dispensing and precision dispensing of adhesives for the packaging of microprocessor devices.

I would expect brass to be an unlikely material for connector pin, since it is typically hard to solder to. Short of changing to another connector or asking the supplier to change their process to plating after all cutting and forming of the lead, you can investigate more aggressive flux options. Bear in mind, more aggressive fluxes must be fully cleaned away after soldering.

John De Leeuw
Manufacturing Process Engineer
TE SubCom
John has more than thirty years of precision metal fabrication, contract manufacturing, fiber optics and electronic manufacturing experience in quality and production management and process engineering capacities. He has been a Certified IPC Trainer for more than ten years. He is currently a Manufacturing Process Engineer for High Reliability Optoelectronic assemblies used in undersea fiber optic cable systems.

There is only one solution that I could recommend. As you are trimming and forming the leads you are exposing the underlying base metal. Pre- tinning pre selective soldering is IMO the only solution you currently have available to solve you problem without going into the use of more aggressive flux. Changing connectors will not necessarily resolve the issue as trimming and forming is still going to expose the base metal.

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.

The simple way out of this problem is to contact a company that can tin the leads with solder at your choice and then run the parts through your process. Unless you are a metallurgist that knows everything about melted metals, it would be pretty much impossible to guarantee a conforming solder connection.

Another easy way out is to find another component that can be processed without issues and that it is also agreed upon by your customer.

Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
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