I haven’t posted much in the forum, let along start a new thread. I guess I really haven’t had a compelling reason to do so.
I had a cheap chinese board for my first electric skateboard, and I’ve just been gathering information for my first build. A unique position that I hold is that I work in an ultrasonic testing laboratory (Non-Destructive testing). We have also recently acquired an x-ray machine and I’m being trained on how to use it.
A few months ago, my cheap esk8 went from ~50% charge to 0% abruptly. From the title of the thread, you can probably guess that it was the BMS. Luckily, I was close to my car, so I didn’t have to push it too far.
Cutting all the junk out, I decided to bring the old BMS in to my office and run a few scans, both Ultrasonic as well as X-ray. I just wanted to share them with the group.
First, the ultrasound will give bonding information about the internals of the package. In this case, the red is bad (air inside) and the gray-scale is usually good.
Here, there is some minor disbond on the leadframe, but nothing too bad. With exception to the left side of the left module, it would probably pass the standards which are commonly used by us.
Then I looked at it with the x-ray machine and had a different story. There are voids in the FETs at their solder to PCB, as well as their Die Attach.
As @Slak reiterated, it is Non-Destructive, assuming that the sample isn’t killed by immersion into water.
There are two types of images above, the first three from Ultrasound and the rest from X-ray. Ultrasound (my current specialty) requires immersion in water, as ultrasound above 10MHz doesn’t propagate through air, in much the same way that sound in our audible range doesn’t propagate through the emptiness of space. This water is just a couplant, or medium, for the sound. X-ray does not require such things, as it is light, and can be used on a dry sample.
The x-ray can see these small voids within the solder, as well as misplaced wires, leads, etc. Ultrasound can pick up on thin delaminations (air gaps/air voids) within the samples. They are very complimentary in their application.
When I first started here (6 years ago in ultrasound inspection), it was odd to me to place the samples in water, but as long as the device isn’t powered while in water, it should be alright if baked out afterward.
@pixelatedpolyeurthan This can be done with other boards as well. These testing methods are used primarily as either Failure Analysis or Quality Assurance methods. We have some manufacturers using our equipment on a few failed samples, spot inspections on a few live samples, or up to 100% inspection.
@ducktaperules Unfortunately, we have ceased all human sacrificing, as the paper-work was becoming too much.
I had a good look for this focbox today but couldn’t find it. I’ll be unpacking all the boxes from that room on the 3rd of Jan. When it turns up I’ll message you for where to send it if you’re still keen to give it a look over.
@Arzamenable I will assume for the moment that you are talking about the ultrasound images. We use a single transducer, pulse-echo type setup, generating the image by a simple rastor scan. Typical range of frequency is 10-230MHz.
While the transducers are labeled at 50MHz, for example, the 50MHz refers to the center frequency. In order to have the Pulse in the Pulse-echo, we need to take the sin wave from one frequency and add in other frequencies, thus developing the pulse needed.
