What is Causing Long-Term Soldering Joint Cracking in Automotive Application?



What is Causing Long-Term Soldering Joint Cracking in Automotive Application?
We are seeing field returns due to solder joint cracking on the pin of a 16-pin through-hole connector. What might be the cause of the joint cracking? Phil Zarrow and Jim Hal. The Assembly Brothers, address this question.
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
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Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

Transcript


Phil
And welcome to Board Talk with Phil Zarrow and Jim Hall, The Assembly Brothers. Here to answer your process, assembly, and other fundamental questions of life. Today Jim, our question comes from D.N. We are seeing field returns after a year in the field due to solder joint cracking on the pin of a 16-pin through-hole connector. The boards are used in automotive dashboard applications. What might be the cause of the joint cracking? The connectors are soldered manually. Could selective soldering offer more consistent solder joints and thus reduce or eliminate the cracking?

Jim
Field returns after a year in the field, it is an automotive dashboard application and it solders when cracking on the pin of a 16 through-hole connector. There are cracked solder joints on a through-hole. My immediate thing is probably a design problem because through-holes tend to be very robust. You have the pin in the hole, it is very mechanically solid. You fill the barrel of the hole up with solder when you through-hole solder it.

They are pretty tough to crack. It has been a year. This is not a defect coming out of the factory. This is a long-term reliability issue, so I am thinking there is a design issue with the board and the connector, the application, and so forth. Otherwise, it shouldn’t make it through a year in an automotive application.

Phil
I agree with your line of thinking Jim, but I would also add don’t rule out possible outside insufficiencies, defects in the actual quality of the materials you are dealing with. We have seen, on numerous occasions, situations with plating problems, plating on leads, plating on connectors. Recently had one on one set of through-hole connectors the gold was actually too thick. Another situation, very similar, there was some contamination in the plating process. This stuff happens.

We have seen in our practice a number of cases where the root cause was due to plating. Plating processes out of control. Some of you on the board level are certainly familiar with black pad, consider black pin. Definitely look at your design parameters and then also take a look at the situation with the actual materials. Don’t be afraid to look upstream before you poke your eye out with a sharp stick. Jim, anything to add to that?

Jim
The final question, could selective soldering provide more consistent solder joints. Yes. With manual soldering you are as good as your soldering technician on that day, at that hour, at that minute, and so forth. Whereas a good, properly maintained soldering process should give you much more consistency.

Will they be better or worse? It gets back to the idea of what it takes to crack a through-hole joint on a 16-pin connector after a year. I have trouble believing that it is a manual soldering problem that would last that long and show up on any kind of a consistent basis. I assume this is not like one 16-pin connector that came in and D.N. is writing to us. I assume there is some consistency in this problem so I would go back to the design and materials as you said, Phil.

Phil
The other thought is was it outright failure or was it an intermittent situation? Oh, we love that intermittent. But the bottom line is you have to get down to the root cause.

Jim
With the through-hole joint, you would think it would have to be intermittent. To good a complete, always open with a through-hole joint is pretty difficult unless the pin is snapped off or something like that or heavily corroded. Again, the automotive environment.

Phil
Of course, this is a dashboard. I don’t know what else is going on down there. A dashboard is not as nasty in terms of the various environmental aspects under the hood. But who knows? Definitely take a look at your design.

Jim
Potentially a condensing environment with overnight temperature swings. And gets back to if there is corrosion on that lead to begin with, long-term condensing environment could activate that corrosion and cause an open area or intermittent.

Phil
But you may need the assistance of an FA lab to actually get down and dirty to find the root cause. Take a look at your design first. Then beyond that, don’t be afraid to look upstream, look at your boards, look at the quality plating on the boards, look at the quality plating on the pins, things along those lines. Especially if you have isolated it down to a connector. As I said, in our experience we have seen some below-par plating so don’t be afraid to look upstream.

Beyond that, all I can add is you have been listing to Phil and Jim, The Assembly Brothers, on Board Talk. Certainly, if you are going to be resoldering those connectors please don’t solder like my brother.

Jim
And don’t solder like my brother.

Comments

Just wondering if the connector solder tails are plated with gold, as this could lead to gold embrittlement, which can cause cracked solder joints. J-STD-001 requires removal of gold plating on component pins with certain exceptions.
Bill Belanger, Janco Electronics, Inc.
Hand soldering should not be allowed for professional electronics, including Automotive, because you will never be able to guarantee that every solder joint have had the correct time/temperature profile. The problems may as well be due to poor plating processes or wrong pin/hole size ratio.

The major cause to the reliability problems is however a not well considered choice of connector interconnect technology. For Automotive applications it for years have been well known that soldered through hole connectors are not the best choice for reliability. Therefore it has become very common - or near to mandatory in many cases - to use press-fit connectors instead.

Some of the benefits are: - Connection technology with the greatest robustness and reliability - High Durability - Gas-tight connection - No soldering defects, flux residues, or similar - No additional cleaning necessary - Efficient and cost-effective placement process
Claus W. Nielsen, E-Consult International ApS
The first thing I look at when the defect is a PTH solder joint, other than the obvious visible solder joint formation on the top and bottom side, is the hole fill. X-ray several of the connectors from the same lot of assemblies to determine if there is insufficient hole fill from a manual soldering issue. Watch the operator who signed off on the soldering operation. Is he/she using lead free solder?

Then check the condition of the annular rings by carefully wicking away some of the solder. Did the lead-free solder leach away the copper barrel or the annular rings, leading to barrel failure and detachment from the drilled hole in the PWB? What weight of copper is being used (for under dash it should be 1/2 oz. copper foil if lead-free solder). Is the operator's dwell time too long?

Did the operator first solder from the source side (bottom side) and then go up top to finish the soldering (if that is even possible) leaving a large gas pocket inside the barrel, with insufficient solder fill? There are a lot of things to look at, but it begins with a good X-ray on a few both before cracking and after.
Richard Stadem, General Dynamics Mission Systems
It would be a rare case that solder joint crack happened inside PTH. Did you verified solder crack by hole microsectioning result or by assumption. If later case, it would be due to ICD(Interconnect Defect) followed by Hole Wall Pullaway. PTH might be too much thermal damaged during solder rework.
Jinho Lee, KETI
Take one of the failed boards and carefully cut away about half of the PCB around the cracked solder joint. Then extract the pin, pulling horizontal to the PCB, without using any heat. If the plating to the pin is not correct, then you will see the base metal exposed on the pin since the plating would still be adhering to the solder on the PCB.

I have seen plating disassociate from the base metal after 2 or 3 years.

Generally to only 'solution' is to use a different manufacturer. Could also scrape through the plating to expose the base metal and then solder to the exposed metal.
Jaye Waas, Renkus-Heinz
I wouldn't be looking at the board plating alone for answers necessarily. What's the hole size to connector pin size ratio? Is there too much wiggle room? IPC has specs on that in 2221. Also look at strain relief on the mating connector. You have some pretty extreme temperature swings in a motor vehicle, and you're using lead free solder, which is brittle. If you're getting good hole fill (probably wave soldering) and your ratios are right, you have vibration and temperature cycles accelerating the embrittlement of your already brittle solder choice. THIS is why aircraft manufacturers get an exemption from the lead free solder regulations. If you can find the vibration source and secure those parts down or isolate them you may be able to get by with not changing the design. You can probably simulate the failure mode on a vibration table. Happy hunting.
Bradley J Fern, Entrust
No picture or other evidence, don't speculate.
Jerry Magera, Motorola Solutions
You need to look at how the connector is mechanically linked to the board. Is the body of the connector retained on the board with screws or some other mechanical strain relief? You can't rely just on the pins of the connector to take all the strain of external wiring or some other attachments, especially in a high vibration environment.
Victor Gold, Rastergraf, Inc.
I worked for an automotive company, where we performed failure analysis on parts that came from the field. We carry out these tests in a conditioned place in the company and we also contract the external analysis service. I definitely suggest analyzing the connector as a raw material, seeing the conditions of the parts in the field and considering carrying out thermocycling tests, accelerated aging in a batch of the connector, this can help them better determine the cause of the failure.
Roger Cespedes, Camtronics

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