manufacturingpcb-assemblysemiconductors
I've seen lots of products with hand painted dots or markings on chips, what do they often mean? Obviously I understand everybody has their own reasons but could it be an industry common practice for QA or programming?
For example, this picture of an Xilinx CPLD has two painted dots. I've also seen ones where it's a sloppy line on the middle of the chip.
When soldering is done by hand there are lots of aspects that factor into how fast it can be done. Here are the largest factors for me when I am soldering:
In general though, I would say it takes me about 45 seconds per part to place the parts on the board. The board can then be baking while more boards are assembled.
Where you have to be careful in time estimating is the time it will take to check for shorts and fix them. There will be errors, maybe just a couple out of the whole batch, but there will need to be more testing time when soldered by hand.
Although tantalum is not one of the rare earths -- it is one of the "transition metals", like gold -- tantalum's scarcity (1 or 2 ppm of the earth's crust) and primary use in electronics (tantalum capacitors) fits in with the scope of this question.
Recent legislation in the US (July, 2010) requires companies to disclose if they are using products with tantalum obtained from the Democratic Republic of the Congo (DRC). As a result, prices have risen sharply as other producers come slowly back on-line. One mine in Australia represents 1/3 of the potential global world production.
(Note: vertical scale of the graph doesn't start at zero, it gives a slightly distorted look. Full size graph is here)
Because electrolytic tantalum capacitors can be much smaller than aluminum electrolytic capacitors of the same capacity, and have higher voltage ratings, they are used in almost all cell phones, and in other portable electronic equipment.
I designed in a couple of 1000 µF "tants" into a product a couple of years ago, and recently the contract manufacturer contacted us saying that the lead time on the parts had stretched out to 16 weeks and asked if I could find a substitute. As a result of this exercise, in my latest design I went back to surface-mount aluminum electrolytic capacitors, even though there was a significant space penalty.
Best Answer
These are put there during assembly and test of the PCB and can mean anything the manufacturer wants to mark.
Often such a dot is put on a microcontroller, when the firmware is successfully programmed into memory. It can also mean, that the device passed all the tests during production.
Whatever the dot means: It is a sign for the manufacturer, that certain steps are done. This makes it easily visible if a board is ready to be processed further, or packaged, or ...