What is the purpose of these markings commonly found on Japanese PCBs?

[HwAoRrDk]

I was just checking out Bunnie Huang's Name That Ware for January, and while examining the photo of the presented PCB 'ware', I thought "oh, there are those odd markings again, and it's made in Japan too". Here's a cropped image of what I'm talking about:



I've only ever seen these kind of markings on boards from Japanese products. Sometimes slight variations, not identical in layout to the above, but always at least two rectangles containing a grid of dots, and two alphanumeric digits. I have another board on my desk right now that is such a variation on the theme. It has, left-to-right, the letter 'M', a dot-filled rectangle, the number '3', and finally another dot-filled rectangle with the lower-right dot missing. On this one it also done in the solder mask instead of silkscreen. (I would take a picture, but it's tiny - about 1 cm width - and my camera has no macro mode.)

I'm sure the dot pattern means something distinct, and not just related to the letter/number, as I've seen several examples of the board I have where the dots change (e.g. centre or upper-right dot absent), but the letter and number is always the same.

Any ideas?

[AndyC_772]

Is there always exactly one dot missing? Maybe it's indicating the board's position in the panel?

[HwAoRrDk]

No, you can see on the example above there are three missing on the left grid.

I highly doubt it's something to do with panelisation, as it's always a 6x3 grid, but a wide size variety in the boards. For instance, the example above is a board that looks to be at least 100mm square, whereas the board I have here now is 50 mm - it's highly unlikely they would both have the same number of boards per panel.

[amyk]

I've seen those too, not necessarily Japanese boards --- the backs of old Taiwanese motherboards sometimes have them too.

Here's another slightly different specimen with a 5x3 and 6x3 grid: http://buckstraders.co.uk/WebRoot/Store30/Shops/9b982c05-e34c-4ceb-95a7-e51b30edb334/5627/6BAA/6D55/302F/6E3B/0A48/3573/681D/20151021_105956.JPG

My guess is that they're date/batch/line code markers used by one common fab. Perhaps someone who actually worked with them will know.

[HwAoRrDk]

Hmm, interesting, that one's got the row of digits along the top, just like the example above. Appears to be room for a 'Z' on the end, which is absent.

[HwAoRrDk]

I've just hit upon an interesting theory...

I was doing some Google image searching for things like "made in japan pcb", "japanese pcb", "japan circuit board", etc. and browsing the resulting pictures to see how common these markings were, and it seemed like all the examples I was finding that had these markings were in some manner associated with Matsushita or Panasonic.



Wonder if this is (or was) a Matsushita thing? And other companies may have copied or adapted the marking scheme over the years.

The only similar thing I saw that wasn't to do with them was an old Namco arcade video game board that had a table with one dot per cell (with a couple dots absent) and two alphanumeric digits beside the table.

[Nusa]

Well, the board pictured in the OP's picture is from an HP printer that's over 20 years old, so this marking system is likely historical rather than actively used. I'm guessing all the other examples are old as well.

[HwAoRrDk]

Yes, some of the further examples I found were from equipment that is pretty old (I think one was even some ISA card from the 80's), but it can't be a long-out-of-use historical practice, as the board I have here right now is at minimum 5 years old, and the top-right example above (the single-layer board) supposedly is a PSU from a fairly recent A/C appliance.

[schmitt trigger]

Purple crypto code? 

Now seriously, I see how the dots would be useful in mapping the individual board's location respective to a panel array.

But as others have mentioned out, this does not seem to be its intended purpose.

[Tomorokoshi]

Indication of assembly variant? Factory code?

[Cerebus]

Is it numeric code represented in some abacus like notation?

I seem to recall that the use of the abacus is still taught in Japanese schools so a representation like that would be second nature to the average Nihonjin but completely opaque to us westerners.

[HwAoRrDk]

I remembered I had in storage a few more of the board on my desk, so I fished them out to check the markings. It's not an assembly, model, variant or revision marker (at least, not for these boards), as the dots differ and yet these boards are all identical.

Also, they kinda throw water on the Matsushita/Panasonic theory, as I don't believe they were made by them. Although, they do feature a relay made by a company since re-branded as Panasonic, so I suppose it could possibly have been some subsidiary. But then again if that's true, why would they use Nichicon caps?...

Is it numeric code represented in some abacus like notation?

Oh, good thought!

I wonder if there is any other Japanese practice or custom that it could relate to. For example (but this doesn't appear to relate to the markings) I know they sometimes refer to years by their relation to the imperial era - e.g. it's currently the Heisei era, so 2018 is 'Heisei 30'.

[amyk]

I don't think it's specific to Matsushita/Panasonic --- the board I posted above is from an Epson printer (although the format of the marking is slightly different.)

[T3sl4co1l]

Probably design or production revision or dating.

The line of numbers reminds me of a similar thing in books, possibly for the same reason.



Incidentally, I've seen a laptop motherboard with assembly variants indicated by dots of glue in a silkscreen table.

Tim

[Vtile]

2 x 18 bit barcode dotcode.. huh?

[TerraHertz]

I always thought these dots indicated refreshes of some tooling used in production. New silkscreen, etc. Because when replacing those, there's no facility to apply new numbers. A dot is easy...

You sometimes see the same thing in injection molded plastic items. Somewhere inside there'll be some model and part number, type of plastic, perhaps a date or sequence code done with rotatable plugs in the mold, and then little engraved dots to indicate rework or checks of the mold.

[Brumby]

Skynet has been sending out it's programming to take over the world one bit at a time... 

[kjr18]

They are also in Yamaha DME32, you can see them in Dave's teardown video:
https://youtu.be/rWBjeB9JP3Y?t=1003

[helius]

I just saw these on a Volvo car radio, the most likely OEM being Alps. I was also reminded of printing sequences and injection mold indicators.
Most likely the PCB marks started as actual silkscreens, and so are a negative code. The screen is originally exposed with all dots on the left and the right, and then the operator applies lacquer to block some dots so they don't print through. I don't have any evidence for what the dots stand for, but it's easy to imagine they could be related to batch runs as the silkscreen is reused and further dots are lacquered over.