[TenTec] Orion 565 failure due to electromigration of solder

[A R]

Gary,

You're right. I should not have attached a moniker to the mechanism causing the observed condition. But, the condition observed was unlike any "whiskers" condition I observed during the early 70's military and space avionics and electronics manufacturing. Back then, we referred to the "whiskers" as "dendritic growth". The differences between the condition I observed on the Orion's board and the whiskers observed in my former life are:
1. Whisker growth of the 70's that I observed occurred only between conductors, and had to be scraped or skived to remove.
2. The conductive substance on the ORION's board surrounded the TXEN pad (not just between that pad and other proximal pads), and the substance was easily removed by wiping.

What was the root cause of the condition on the ORION board? Don't know. What, exactly, was the substance? Don't know, since it wasn't subjected to a material or SEM analysis. The board appeared to have been as originally manufactured, with no evidence of repair or rework, and no flux residue. It took something over 10 years for the condition to develop/propagate to the extent sufficient to cause circuit failure. Some sort of board material property issue? Don't know. Some sort of board surface contamination during original manufacture? Don't know. This ORION has lived it's life in a sanitary, clean (not Class 1 clean-room clean), dry (Arizona), air-conditioned environment.

73,
Allen--W7GIF



----- Original Message -----
From: Gary J FollettDukes HiFi<mailto:dukeshifi at comcast.net>
To: Discussion of Ten-Tec Equipment<mailto:tentec at contesting.com>
Sent: Sunday, October 16, 2016 9:39 PM
Subject: Re: [TenTec] Orion 565 failure due to electromigration of solder


The definition of electromigration is migration of conductor material in a circuit trace due to the momentum transfer from charge carriers (usually electrons) flowing in the conductor traces and the phenomenon bears characteristics of diffusion. The species undergoing electro migration need not be ionic, or charged in any way. The electron flow is simply pushing the conductor metal out of the way.

Electromigration CAN NOT TAKE PLACE in the absence of significant current density flow in the conductor in question.

In electromigration, conductors migrate atomistically in a direction orthogonal to a current flow, causing flow of conductor material in a path that leads away from the conducting trace. This phenomenon can cause either a short circuit to an adjacent trace or an open circuit in the trace if sufficient material migrates. Much effort to reduce this effect, especially in Aluminum metallization in IC chips, was undertaken in the late 1970’s. Electromigration on the macro scale, the size of PC boards and associated parts, has never been documented.


More likely what you saw was solder whisker formation, a recurrence of what took place decades ago with low Lead solders and which is coming to the foreground once again with Lead-free formulations. These whiskers can grow due to heat, stress and other environmental stresses, mostly in purer metals, but can also take place in certain alloys (no need for current flow) and cause the formation of short circuiting bridges as you describe. The small sizes of the whiskers, on the order of the wavelength of light, is what gives rise to the whitish appearance. These types of whiskers caused failures in satellites and in some nuclear power plant metering systems. The term “electromigration” is incorrectly applied to this phenomenon even in Wikipedia. They correct their mistake later in their discussion when they point out that no current flow is required for whisker formation to take place. Current flow is required for electromigration to take place, though the current can be a corrosion current in an appropriate corrosion cell.

They do show some pretty cool images of such whiskers, many of them several millimeters in length, more than enough to cause the problems you experienced.

If you had a small sample of the stuff you removed, I could send you some nice scanning electron microscope images of them along with their compositions… That would take about 15 to 30 minute of my time.

73

Gary


> On Oct 16, 2016, at 10:48 PM, A R <raf_3 at msn.com> wrote:
>
> Just recovered from a failure of my Orion 565 that looks to be a result of ionic solder migration.
>
> Orion was purchased two years ago from original owner's estate. Details of his operation/use are unknown.
>
> Replaced snaphat battery, A9 caps, and intermittent VFO encoder. Orion performed flawlessly for over a year following those measures, and was relegated to back-up status about 3 months ago.
>
> When it was brought back into service, receiver worked fine, but no transmitter output on either ANT 1 or ANT 2 outputs. Two master resets were performed, but no joy. Covers were removed, and interior subjected to the burnt component "smell test", and visually inspected for any obvious causes (loose cable connectors, etc.). Discovered powdery substance on the I/O board that surrounded the entire periphery of TXEN 1 rca jack solder pad (perfectly circular around solder pad) intersecting the adjacent +13vdc wire conductor solder pad, with a "track" extending to ground side (anode) solder pad of adjacent 5KP15A surge suppressing diode. Removed the powdery deposit using Q-tips and 90% isopropyl, followed by judicial flushing with distilled water.Gently and slowly dried with warm (not hot) air, and after 10 minutes of ambient air dry time, applied power. All sytems are "go", and the Orion lives again.
>
> I have never used the TXEN or TXOUT jacks, but don't know whether the original owner did. At any rate, the condition (which I attribute to electromigration of the solder) had to have resulted/propagated with no externally applied potential to the TXEN jacks, since the condition only became "fatal" after two years of problem-free operation/life. The internally applied potential to the TXEN pad/lead is just +3.3vdc. And, the distance from the TXEN's pad edge to the diode's anode (ground) pad edge is more than 1/2 inch, and distance from the +13vdc pad edge is approx 3/16 inch. Since the deposit was uniformly centered around the TXEN's pad (and, not the +13vdc pad edge), it would seem that the donor was the TXEN pad/solder.
>
> Given the wide spacing between these pads/solder and the low potentials involved in this case, the potential (no pun intended) for similar failure conditions elsewhere (with closer pad separation) would seem quite possible. So...I guess my counsel is to do a close visual inspection (under magnification) of boards when unexplain/unprovoked failures occur. Or, maybe better...periodic visual board inspections...or, even cleaning...BEFORE electromigration causes a failure. Fortunately, in this case, the condition didn't result in permanent (and catastrophic) damage. An ounce of prevention....etc.
>
> 73,
> Allen--W7GIF
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