Now I am down to just the main PCB, well actually it is two PCBs there is a small board mounted to the back of the main PCB.
This is the front and back of the small board
On the rear you have the battery terminals (Across the middle) the cassette eject switch and four other switches that go to the side of the camera, together with audio jacks, and a bunch of capacitors and individual transistors. On the front of the board, there is a single power transistor (B1202 which is a 50V 3A PNP transistor made by Sanyo) and one 16 pin ic a Mitsubishi 7618N with a week 12 1994 date code. I can find nothing on the web about this part so lets decap the part and take a look.
Its a 2.4mm x 2.0mm single metal Bipolar device. Once again I notice there is no visible die seal, (Although this time there is a sizable piece of silicon between the saw edge and the die oxide edge) it looks like the die seal wasn’t so common on chips in this era.
Update: As noted in the comments the chip is from Fuji Electric and is a buck-boost controller referenced in US patent 5402060
Its function is not clear to me, it is on the board with the battery connection so you would expect a voltage regulator on the board, but I think it has too many pins for that. There are 9 beefy output transistors visible (Down the right side, and top middle), the chip is also surrounded and connects to six switching transistors on the board. It is also close to the cassette ejection switch which appears to connect to it, so I think it might be a driver chip associated with driving the small motor on the tape assembly that guides the tape around the head.
Now onto the main board. First off you can see the board is dominated (Vertically) by the rectangular component at the back that I learnt last week is an Acoustic Delay Line.
Oh my giddy aunt look at the number of chips on that board! I count 12 on the front and 16 on the back for a grand total of 28! I have die photo material for several months here.
Not many of these devices are identifiable, a problem with devices that are effectively pre-internet era (I recall 1994 being a transition year where internet usage started to take off but still very little commercial presence). Here is a the list of what I have found with some speculation
|Matsushita||AN2145NFHP||80||CCD Video Camera Signal Processor|
|Hitachi||A118186||Attached on board under 8838|
|?||5W01||8||Voltage regulator? (x2)|
|Toshiba||TB6504||24||PWM Chopper Type Bipolar Stepper Motor Driver|
|Mitsubishi||M523564FP||48||Motor Driver (?)|
|?||15218 XRDJ||8||Voltage Regulator (?)|
|?||XRDA 324A||8||Voltage Regulator (?)|
I thought I would take a closer look at the larger IC’s on the board the NEC D78054, and the Standard Micro 78148. I have not heard of Standard Micro and could find zero information about them on the internet. Since it was close to the NEC MCU I thought the chip was likely DRAM. As this is early 90’s vintage I thought it would be interesting to see what early 90’s DRAM looked like.
Well it was a bit of surprise when I decapped the part and found it to be a very large MCU also made by NEC! So was Standard Micro an NEC brand for some of their MCU’s? It’s all very strange. Unlike the D78054 no datasheet could be found for this MCU.
The die is a large chunk of silicon at 10.2mm x 7.3mm and has lots on interesting structures
Looking at an area of general logic I measure the polysilicon gates to be ~1μm, and surprisingly even for 1991 just one layer of (Al) metal. A 1μm CMOS process was quite advanced around 1990, but two or three metal layers were more common.
Here is an example of an interesting circuit layout with lots of symmetry (No idea what its function is though)
You can see in this image where the designers had to compromise due to having only a single metal by using polysilicon as an interconnect layer. Throughout the die there are examples like this where tracks are joined by wide (Sometimes very wide) links of polysilicon.
There are three different memory types on this MCU, and going back this far with a 1μm process the feature are big enough that you can start to pick out some structures in the memory array with an optical microscope. This is what I think is a 6T SRAM (The block on the far right of the die photo)
I think this block on the die is ROM.
The large memory array on the die is I think EEPROM (What later became known as Flash) I can just make out horizontal polysilcon lines with vertical crossing (Of what might be silicon nitride or another polysilicon line) creating storage nodes with vertical metal tracks with only a few rows of contacts.
This Standard Micro/NEC 78054 is in a quadrant of the board labelled SysCon so it is likely that this is providing the system control functions, but I do not know why they have two MCU’s on the board. Perhaps the second one is related to the video signal processing, but there is Matsushita (AN2145) CCD signal processor (that I have not yet decapped) beside it and the recording system is an analog signal process so I can’t see why they would want an MCU for that.
The NEC 78054 has a die mark indicating it was designed in 1992 and a datasheet exists for it
It is significantly smaller the the other MCU at 6.19mm x 5.43mm but even from the die photo you can see it has significantly denser layoutThe large memory block at the bottom is 32kb of ROM, with 1kb SRAM array above that. The gates are sub-micron so I believe this was fabricated on a 0.8μm 3 metal CMOS process, so just one generation more advanced than the other MCU. It makes an interesting comparisonLooking at the standard cell/general logic area imaged above the gate polysilicon is harder to see with more layers of metal interconnect obscuring it. It is also white (cf. a grey appearance on the previous MCU, this is consistent with the gate being silicided likely with Titanium (Or possibly Cobalt) which was done starting around the 0.8μm to reduce the gate resistance.
Here is the SRAM array (focus stacked image with 80x objective)And this is the ROM array you can clearly see the tighter geometry used.I am going to conclude this marathon teardown here. I will depot and image some of the other die on the board and publish the die photos over the next few weeks/months in between other teardowns.