CT takes time, but can virtually microsection and analyze any plane in an entire sample.
2-D offline x-ray inspection of electronics is directly analogous to 2-D medical x-ray imaging, the only difference being image magnification is required to see the much smaller features within electronic devices and boards. (Also, the sample doesn’t talk back!) Medical x-ray imaging also offers CT scanning (also known as 3-D x-ray or computer tomography or CAT scans), and the same technique is available for electronics analysis. From Greek, tomography means writing slices.
CT provides a 3-D density map model of the sample from which virtual 2-D x-ray slices can be taken and examined in any plane within the model. Consider it like being able to take virtual microsections anywhere, at any angle and as often and repeatedly as desired through the sample without having to cut, pot, polish, optically image, repolish, re-image, etc., as when making a traditional microsection. 3-D representations of the sample may also be created and virtually sliced (FIGURES 1 to 3).
Everyone has an x-ray system for BGAs. Why not use it for through-hole too?
I am often asked about the use of x-ray inspection to investigate issues with surface mount components. Quite naturally, there is always a focus on BGAs, flip-chips, QFNs, etc., where the optically hidden nature of the joints lends those parts to x-ray techniques for analysis. I am rarely asked about through-hole joints, however. Is this because no one uses them anymore? I don’t think so. Indeed, I would venture to suggest there probably are more through-hole joints made today than ever. I am surprised PTH joints do not come up in conversations more frequently because they are obviously hidden joints.
IPC-A-610 guidelines qualify the level of hole fill to be expected within these joints. How else can you nondestructively check during manufacture if these conditions have been met? Are all through-hole joints made perfectly with 100% fill, and never with any issues? Or, as I suspect, is through-hole seen as a great, but slightly less fashionable, technique, and do many not consider an x-ray system can also quickly and simply confirm the quality of these joints? In other words, you already have an x-ray system for BGAs, so why not also get the benefits of its quality control capabilities for through-hole joints?
Explaining solder joint defects, one interruption at a time.
“Thank you all for promptly joining this morning’s webmail conference call. Today we are going to review the x-ray images our outside lab FTP’d us yesterday. Please set your phones on mute by pressing *6 if you are not speaking, and set your computers to the link provided by the meeting invite. You can unmute your phones in the same way, by pressing *6, if you wish to contribute to the conversation. You may listen via phone link, or by plugging earbuds into your laptops and activating sound. If you feel compelled to speak, unmute your phone and speak one at a time. We’d like to give equal time to as many members of our several participating engineering groups as possible. We have a big agenda, and many participants, so let’s get started.”
Here we go. Amateur hour.
Simple process steps for inspecting arrays. (But don’t expect them to always be the source of failures.)
After more than 15 years working with people who choose to use x-ray inspection as part of their fault-finding and quality-ensuring procedures, the most common refrain I hear is, “The board’s not working; it must be the BGA.” I do also hear this from those who do not have access to x-ray!
Arguably, as the BGA was the first commonly used component to be placed on boards with all its interconnections hidden from any possibility of post-reflow optical inspection, I suggest the BGA has been the primary driver for the increased uptake of x-ray inspection in recent years. After all, x-ray inspection is nondestructive and can see where optical systems cannot. Perhaps it is the entirely optically hidden nature of the BGA joints that has caused its infamy within electronics manufacturing. By not being able to see the joints that have been made, how can the BGA be ruled out as the cause of the failing circuit? Without some certitude in this, how can a contract manufacturer assuage its client’s belief that all non-working products have been caused by poor reflow under the BGA, rather than by some other mechanism? X-ray inspection goes a long way to help both parties resolve this, and, assuming it isn’t actually the BGA’s fault, the “first likely cause of problem” can be ruled out, and all parties can move on quickly and productively to consider other potential reasons for the issue.