Will Foxconn build in Wisconsin?
Its track record in India, Malaysia, and various other places says no, and according to this Washington Post reporter, “No one had gone back to see whether this had been carried through, and it hadn’t.”
Well, not no one …
Most articles discussing the copper-tin intermetallics that form during soldering refer to them as a necessary evil. The evil being the perception that intermetallics are brittle and can lead to failures in thermal cycling or drop shock.
I view the situation differently. From my perspective, the formation of copper-tin intermetallics is the miracle of soldering. Look at it this way, to assemble electronics, bonding copper to copper (the leads on the components to the pads on the PWB) in the presence of polymers (the PWB epoxies and the component cases) is required. These polymer materials can only take about 250°C for a few minutes. Copper melts at 1083°C, so bonding copper to copper in the presence of polymers would appear to be quite a challenge. Enter tin-based solder.
Lead-free (tin-based) solder, say SAC305, melts at about 219°C. So, with a peak temperature of about 245°C, in the reflow oven, solder can be melted and form an electrical and mechanical bond with the copper in the leads and pads. At 245°C, the many polymer materials are unharmed for the 90 seconds or so that soldering requires at this temperature.
But, what about the material properties of the intermetallics that are formed? Aren’t they too brittle? Lee et al* performed analyses that suggest that the intermetallics formed in soldering are not brittle. Their work also suggests that the failure modes are not in the intermetallics, but in the interfaces between the intermetallics and the solder, copper, or the different intermetallic compounds, Cu3Sn and Cu6Sn5. These two intermetallic compounds are shown in the figure below.
Copper tin intermetallics from Roubaud et al, “Impact of IM Growth on the Mech. Strength of Pb-Free Assemblies,” APEX 2001.
It has long been assumed that the thicker the intermetallics, the greater the risk of failure due to the intermetallic thickness. Lee’s work would appear to bring this concern into question.
Stay tuned for a continued discussion on intermetallics and their effect on reliability.
*Lee, C. C. et al, “Are Intermetallics Really Brittle,” IEEE Electronics Components and Technology Conference, 2007, pp. 648.
Cheers,
Dr. Ron
I’m saddened to get the news this morning that Jim Raby has passed away. As longtime readers will know, Jim was one of my favorite persons, not just in the industry but in life. What a tremendous fighter he was for doing things right! I will always miss him. 
My sincere condolences to his wife Ellen, son David and everyone at STI on this sad day. We have lost a fine engineer, gentleman and human being.
Our all-things-about-electronics manufacturing standards body, the IPC, specifies the proper numbering order for most components. That’s a pretty nice thing that they do there, but it’s not always enough to prevent layout mishaps. Case in point a line of small PCB mount switches.
IPC calls out pin numbering for dual inline components, with pin one on the upper left (at zero degrees rotation), counting down, then over to the bottom right, and counting back up, as in the illustration below.
Given, that, it would be logical to assume that all dual inline components follow the same pattern. Logical, yes. Accurate, no. Multi-color LEDs, connectors and switches are some of the more common offenders.
In this particular switch, it’s not just a case of the numbering not following convention, it’s also different from one variant to another. I understand why. The switch isn’t changed between through-hole, top mount surface mount and side mount surface mount, but the leads have to be accessible from different parts of the package.
The following two footprints are from the same switch. One mounts on its side, and the other, standing up.
The pin one numbering doesn’t follow convention, nor does the numbering of pins 4 – 6. And, you may have also noticed that the two are top-to-bottom mirror images of each other. Ugh.
This is why my mantra is: Always check the datasheet. Always.
Duane Benson
Don’t take it for granite either, because granite is too heavy.
There are a lot of components that require special handling. Some days, “special” requirements seem more the norm than the exception. But, every now and then, we see something that puts even those special components to shame.
Not long ago, we received a parts kit that contained a component so fragile, that most of them didn’t survive the trip with the shipper. It’s a 10 x 9mm (well, actually 9.68 +0.00/- 0.08mm x 8.64 +0.00/- 0.08mm, to be precise) sensor that’s only 0.05mm thick. That’s 1/4 as thick as the diameter of the solder balls connecting it to the PCB.
The part has solder balls on the silicon, with no other packaging. The dice has to be that thin, as the light-sensitive area is on the other side. That doesn’t make for a very robust component. It would require special handling all around. Unfortunately, no matter how careful we might be, if they’re broken when we receive them, there’s not much we can do (other than take pretty pictures).
In taking these closeups, I noticed that the registration in ball placement isn’t all that great. In the image below, take a look at the ball on the left, second from the bottom, and the ball on the far right.
The datasheets call out all non-specified tolerances as +/-0.001mm. With these being 0.2mm diameter solder balls, I’d have to say this is way outside of that tolerance. I’m sure the part would have adhered to a decent board just fine, but if the PCB were off a similar amount in the opposite direction, you may very well have a problem.
Duane Benson
You could make a very tiny sundial out of this.
But, could you use the shadow parallax to calculate the distance to the sun?
http://blog.screamingcircuits.com
Apparently someone has decided to toy with New York state by assuming the role of “Foxconn US” and trolling a poor soul named Chris Souzzi, who works for Genesee County Economic Development Center.
I’m no fan of Foxconn, and I don’t think there’s a snowball’s chance in hell they put a plant in the Empire State, but stunts like these aren’t funny (even if that’s what’s intended) and simply go too far.
I cannot express how pleased I am today at the news that my former colleague and (still) good friend Kathy Nargi-Toth has been named president of Eltek USA.
Kathy is one of the warmest and kindest persons I have had the pleasure of coming across, and her industry knowledge is second to none.
I wish her all the luck in the world in her new job — not that she will need it!
With each year comes a new model of the Apple iPhone. And like clockwork, a few months before the product release, purported images and details of the new phones (and other Apple products) start showing up on various social media.
Would it be right to be suspicious that these “leaks” are simply ploys to generate interest?