Ask the Experts
April 26, 2023 - Updated
June 24, 2015 - Originally Posted

Tough Hand Soldering Problem

I work in an auto glass factory and we're having problems soldering the defrost cable wire to the windshield grid pattern. I think it has to do with factory temperature as it is very hot over 100 degrees F.

It is also extremely humid with levels reaching close to 100 percent. My bosses keep blowing chillers on the glass but with little effect. What can we do to improve the solder connections.


Expert Panel Responses

Without more information its very hard to say, but with 100% humidity and chillers being blown onto the glass I would of thought you would have been causing condensation to occur which is not what you want.

If it's that hot and humid are you suffering with an oxide film on the metal surfaces you are soldering? More information on the actual fault or picture would be really useful.

Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

The cooling may be causing more of an issue. Remember the grid pattern is a heat sink. If you are having problems with soldering to a large thermal mass then increase the temperature of the grid to allow for better soldering temperature at the point of connection and preheat the surface.

But first you must make sure the surface of what you are soldering is solderable and not oxidized do to the environment. These working conditions will oxidize the surface and if you are using a very low activation No Clean Flux that may not be aggressive enough to remove the oxide.

There are ways of determining these issues and setting up DOE's to screen out the effects.

Terry Munson
President/Senior Technical Consultant
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.

To offer possible solutions I would need to understand the surface finishes, solder materials and details about your process methods. In general it is not good to have high humidity where to process or store components.

Stephen Schoppe
Process Sciences, Inc.
Stephen Schoppe is President of Process Sciences, Inc., and has 19 years experience providing SMT services to electronics manufacturers. Stephen provides consulting to several Fortune 500 clients on solder and SMT processes, and is a frequent guest speaker at SMT industry events.

Usually this type of application requires a large amount of power to be applied directly to the thermal load. Glass is an excellent conductor of heat and is drawing the power from your soldering tip faster than it can be replaced by your soldering system. To make matters worse, you are trying to cool the glass with an external chiller.

I would suggest a Direct Power Soldering System with a dual heater soldering cartridge. This system would be able to deliver up to 160 watts of soldering power directly to the soldering tip through the dual cartridge/heater setup. This will ensure rapid heat up to solder the joint without damage to the solder or the glass.

The part number of the hand piece is MX-HPDC, you can find additional information in a web search.

Edward Zamborsky
Regional Sales Manager
OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

Without knowing the exact type of soldering problems you are having, I can only hypothesize based on your description of the application and the conditions. First of all, you state that the environment is 100 degrees and up to 100% humidity. That type of environment can cause oxidation of metal surfaces very quickly if they are not gold plated. The result would be dewetting or non-wetting of the surface you are attempting to solder to.

You can try to clean the surfaces prior to soldering either chemically or with a mild abrasive (like a Scotch-Brite pad). You could also use a more aggressive acid based flux during your soldering operation. If you do this, make sure that you have a way to thoroughly clean the joints after soldering to remove all flux residue. If you leave any acid flex residue behind, your solder connections will corrode over time.

The other thing you mention is that you have cold air blowing on your work area. That is going to keep the surface cool and can complicate soldering. How are you going to be able to get the solder to flow and fuse to the surface if you are blowing cold air on it? Having an elevated temperature of the area to be soldered should actually improve the ease of soldering because the total temperature rise to get the solder to flow is reduced. I would recommend that you redirect the chillers away from the area you are soldering.

Mark Finstad
Senior Applications Engineer
Flexible Circuit Technologies
Mark Finstad has over 30 years in the flex circuit industry in both design and manufacturing. He is a regular speaker at IPC APEX (Professional development courses) and PCB West (flex circuit design courses). He is also vice chair of IPC-2223 and active member of IPC-6013. Finstad has extensive experience with both domestic and off-shore manufacturing.

Its a little hard to trouble-shoot your soldering problems without knowing more about the metals you are using, the solders and the fluxes, but one thought I had was that you are getting contamination on the metals prior to soldering.

The contamination could be dust or particulate, finger print oils, or some sort of manufacturing debris that just settles on the metal surfaces. While it is a little unusual to pre-clean the solder pads before soldering, it is not unheard of, and since your application and environment is so extraordinary it might be a useful experiment. Even a little contamination on a solder joint can affect the quality of the joint and it's mechanical durability.

I would suggest pre-cleaning with a pre saturated wipe, such as the Economy Wipes from MicroCare. They're a good choice in your factory because - unlike most pre saturated wipe packaging - the MicroCare package self-closes which keeps the wipes from drying out.

If that's not feasible or cost-effective, try a slow-drying cleaning fluid used with a lint-free wipe, for a gentle but fast cleaning process. I recommend slow-drying because any normal, fast-drying product will simply evaporate too quickly in the 100˚ heat. Products in this category from MicroCare might be the Slow-Drying Citrus Flux Remover or the General Purpose Degreaser (which has a good flux removal capability).

Mike Jones
Vice President
Micro Care
Mr. Jones is an electronics cleaning and stencil printing specialist. Averaging over one hundred days a year on the road, Mike visits SMT production sites and circuit board repair facilities in every corner of the globe, helping engineers and technicians work through the complex trade-offs today's demanding electronics require.

Assuming wire solder is being used and not solder paste the temperature of the work environment would not be the likely cause of solderability issues.

This particular soldering application is highly specialized and the alloys that are used to solder to the tabs of a defroster grid pattern are usually specific to this application and often proprietary.

If you are attempting to solder with typical alloys such as Sn63/Pb37 or SAC305, you will almost certainly have difficulty regardless of the tools and environment used in soldering.

Tim O'Neill
Director of Product Management
Timothy O'Neill is the Director of Product Management for AIM Solder. AIM Solder is a leading global manufacturer of assembly materials for the electronics industry. Mr. O’Neill has 25 years of industry experience is a Certified IPC Specialist.

Mr. O’Neill’s responsibilities include developing product and technical information; he is a technical writer and presenter for industry trade publications and events and has been recognized as a Speaker of Distinction by the SMTA.

The "land" area for the wire attachment is typically made of the same material as the grid. Depending on the technology used, this can be either a fired-on conductive material (metal/ceramic composite), or a polymer-based conductive material that is printed on and cured, but not fired. Both of these "thick film composition" types can have marginal solderability.

The ceramic-based materials can experience oxidation of the metals during high-temperature firing, and if improperly applied and fired can have high surface glass content, both of which can impair solderability. The polymer materials can have high surface polymer content, and the metals involved also oxidize. Finally, the plant environment where the soldering occurs can affect the solderability of the material if the material is exposed to it for a prolonged period.

In any case, once the solderabilty is degraded, the only remedy is usually mild mechanical abrasion. The old trick for ceramic thick film compositions is to use a pencil (not ink) eraser, which is aggressive enough to remove oxides but not so aggressive as to damage the film. This technique also works for some polymer thick film compositions.

The real goal would be to avoid the occurrence of poor solderability. In order to do so, you need to discuss the problem with the engineers responsible for application of the defroster material. Detailed materials and process knowledge is required to understand how to optimize the solderability of the material, and to be able to direct you as to the impact of your plant environment.

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.

If they can determine the metals to be soldered, thediameter of the wire to solder and the type of wire solder/flux are critical inthe hand soldering process.

Cleaning the solder points just prior to soldering is animportant step.

Knowing the type of metals like 90/10, 90% tin & 10%lead will require a higher solder temp. Also if you use a highly activated fluxcould ease the soldering.

The solder equipment should have a temp range of 350-1000degrees F. Use the correct solder tip and preheat connection then feed wiresolder/flux. Once reflow starts, you will notice the solder melting and fluxevaporating. The flow should be smooth resulting in a reliable solder joint.

Go online an check IPC 610 that has good illustration onsoldering wires.

Robert Freid
President and Founder
Contract Manufacturing Consultants, Inc.
Robert Fried helps leading electronics OEM's develop world-class sourcing strategies for PCBA, cables, precision metals, plastics, modules and complete end-products. Other service areas are supplier risk assessment, comprehensive outsource ...

Reader Comment
There are several factor effecting either negatively or positively the soldering performance. The silver on glass must be cleaned out (burnishing) before to improve the wetting and to remove any impurity. Humidity is of course an important point to keep in mind, however, more important is the silver characteristics and its firing degree during tempering process.

Check your entire soldering process, I would recommend a direct electrical discharge with a controlled resistance system to deliver the energy as fast as possible and in such way avoid glass acting as a heat sink. The best burnishing method I have seen is using a fine fiber glass stick, it removes the dross and any contamination on the silver like sulfurs. Flux is better when using a rosin based flux mildly activated.
Hugo Perez Whitaker, Antaya Technologies Corp

Reader Comment
This should be a reasonably easy task. The contact surface needs to be burnished with 1500 - 2000 grit sandpaper. The alloy should be 62/36/2 (2% silver). The iron must be meticulously clean and well tinned with the alloy being used for the connection.

The allow retains the eutectic quality with increased conductivity due to the silver content and has a melting point of 315 degrees C. I use the Kester 24-7150-0018 which is an activated rosin solder. Works quite well and produces a clean flow with a shiny appearance.
Marc Lewis, CET, Quantum Technologies, Inc

For soldering to large glass panels, solar panels, diachromatic and ultrachromatic glass, aluminum panels, ceramics, and other large heatsinks I use either laser soldering or ultrasonic systems. I have had just super results using ultrasonic solder systems like Unix shown here

As well as smaller hand-soldering systems.

There are others out there I have yet to try, but ALL of them will allow you to try out a system to ensure you can develop a process that works before you invest in the equipment, and many will even develop the process parameters for you if you provide access to a sample.

Soldering directly to glass, ceramic, silicon-based substrates, etc, is actually possible using a US solder system, although you are not really soldering in the sense of the word in that no intermetallic formation is made, but rather a bond between molten solder or other filler materials into the porous substrate, where it cools and "grips" the substrate with surprising strength. But for foil on glass, or foil on silicon as is done on solar stringers, windshelid antennas, solar glass, etc, that is a very common practice, but a very specialized process also.

Contact Japan Unix or S-Bond, Inc. I am sure they can help you. Good luck.

Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.

Reader Comment
You have provided some of the information needed to troubleshoot this process but not all. I would need to know the alloy, flux type and heating method (solder iron, hot air, hot bar?) to be sure. Based on what we know, it is probably an oxidation problem with the grid. You could try a quick cleaning prior to soldering and measure teh results. You may also be using the wrong flux and/or wrong temperature and/or wrong heating device. The high humidity is almost certainly causing problem with solderability. Also, cooling the windshield and grid will not help, in fact it will hurt the soldering process. The windshield and grid are a high mass heat sink and cooling only compounds that problem.
Bob Doetzer

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