The Ware for April 2025 is two digits out of a TI-55 calculator display. The full display assembly and calculator IC can be seen below.
This was my father’s old calculator that he got back in 1979, which I recently recovered and lightly modified so that I could power it from a USB plug. I was getting frustrated with how buggy the “standard” calculator apps were, and this thing is perfect for doing taxes – I can crunch numbers without any fear of data being sucked into the cloud, or ads popping up. Even after 46 years, the TI-55 performs flawlessly – I can only aspire to build products with such evergreen utility and service life.
I took it apart, as I do to almost everything within arms reach of me, and was amused by the bonding error on the LED display. I’ve seen wirebonds repaired by hand before, my guess is someone in Taiwan back in 1978 spent a hot second pulling off a failed bond and redoing it on a manual bonding machine.
I thought it was interesting to include some more photos of the components because even back in 1970’s, the global nature of the supply chain was clear. Here is a calculator from “Texas Instruments”, but the chip was packaged in Singapore (probably not more than a half hour from where I live now!) and the display was bonded/assembled in Taiwan.
People speak of the outsourcing and globalization of electronics as some sort of recent phenomenon, as if electronics manufacturing plants were all originally in the USA, and only in the past couple decades migrated to Asia. However, if this calculator is any indicator of how supply chains worked almost 50 years ago, the outsource assembly of electronics to southeast Asia would seem to be a time-honored tradition dating from the dawn of consumer electronics.
The keypad backing and plastic case bear “made in the USA” marks. So, while the semiconductors were packaged up in Asia, the injection molding and final assembly was done on a line somewhere in the US; the injection molder is identified as “Majestic Mold”. Injection molding is a whole separate and also very interesting supply chain story, but the short version is that I have seen some high-end specialty lines in the US (mostly medical and aerospace stuff) but the ecosystem of skilled labor, tools, raw material suppliers, machine repair specialists, recycling facilities and trade-secret know-how necessary to support cost-competitive injection molding has largely relocated to southeast Asia since the turn of the century.
I’ll give the prize this month to Adrian (unfortunately by the time I got around to clicking Joe’s image links, they were all 404’s). While nobody was able to guess the exact make/model of the LED, I did appreciate the image Adrian posted of a functioning display on his mastodon account. I was wondering what the “fingers” were on the metallization, and his image made it click for me. My guess is that the carrier lifetime was short enough on these older devices that regularly spaced fingers were needed to ensure uniform current density in the active region of the LED. Charge carriers can travel farther in today’s more pure wafers, and so modern LEDs don’t suffer as much of a brightness penalty from metallization blocking the active area.
