Rohm BA6860FS 3-phase Motor Driver

Package

From 1994 another chip from the JVC Camcorder.  This one was located on an area of the board labeled “SERVO” so I guessed it was a motor driver.Rohm BA6860 Motor DriverI was somewhat surprised to manage to find a datasheet.  Turns out it is a 3-phase motor driver for the capstan motor (The motor that drives the tape movement spindle) in the Camcorder.

Die Photo

The die photo is quite good looking. The die is 2.97 mm x 2.83 mm (8.4 mm2) and is made on a 2 metal (Aluminum) Bipolar process.Rohm BA6860FS die photo(click on image for higher resolution image)

The driver transistors for the 3-phases are clearly seen in the top right. This is the block diagram from the datasheet The pinout is quite strange (Even though pin 1 is annotated on the die) and I was not able to figure out the pinouts so can not make out the block functions.

Still a nice looking die though.

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Motorola MC6802

A few months ago I looked at a Motorola MC6800 bought on eBay that was branded with a Freescale logo, contained an Hitachi fabricated die (probably from late 80’s or early 90’s) and had a 2016 assembly date code.  Reader Jeremy wanted to compare a real vintage 6800 and kindly ordered this MC6802 for me.

I can make out from the very worn and faded markings

MC6802L  P1H852

Which I believe is a week 52 1978 assembly date code. Released in 1977 as an upgrade to the MC6800, offering an internal oscillator and 128 Bytes of RAM.

 

Thus assembled almost exactly 39 years ago prior to the date of this this post. It is a truly vintage part, packaged in a ceramic DIP.  I popped the lid off using a blowtorch to melt the solder. I also used a strong magnet to pull the lid off (To avoid damaging the die.)The die is soldered to the lead frame, one interesting feature the ground wire has two bond wires, one going to the die, another to the lead frame, but rather than bonding directly to the gold plated lead frame it is bonded to very small piece of silicon or metal – I can’t see why they did that.As it is in the package I am able to take a die photo with the bond wires intact.  The package depth limits me to the 10x objective for the die photo.  The working distance of my high magnification objectives is too small to focus on the die in-situ. To zoom in on the features I had to remove the die from the package.

MC6802 Die PhotoMC6802 Die Photo

(click on image for high resolution version)

Back in 1978 3″ silicon wafers was state of the art.  With a die size of 5.55mm x 4.96mm I calculate they would have had 99 candidate die per wafer.  They were probably doing well to yield 25-30 die per wafer at the time. The datasheet also mentions an MC6808 which was identical to the 6802 but without the 128 Byte RAM, so they obviously recovered some failed parts where just the RAM was defective to gross more parts per wafer.

The die has a distinctive and unusual monochrome look to it.  I removed the die (By heating the package on a hotplate and carefully sliding the die off of the solder. Which proved tricky to do with a very hot die and without a jig holding the die still.

You can see the pitted/mottled texture of the oxide layers which is obscuring the poly and active areas. The latter can be tricky to see in some structures.Normally the oxides are transparent (It is effectively glass), since this was sealed in a ceramic package, it must have come out of the wafer fab looking like this.  I have seen this once before on another old Motorola part.  So clearly it is a characteristic of the process Motorola used. It’s unfortunate for us as it makes viewing the structures quite difficult.

The main die logo is very visible confirming this is pucker Motorola MC6802MC6802 Die Logo

Not so visible, hidden under the mottled dielectrics there is another die mark R1H.  Could that be Ray Hirt sneaking his initials onto the chip (He is one of the designers referred to on the MC6800 Wiki page) or is R1H for something else?

MC6802 Layout

One aspect of taking the die photo in-situ is that it makes identifying the pin-out much easier.  Here is the die photo with pin-out labelled.MC6802 pin-outYou can see the internal oscillator pins on the the top left side.  T he ROM that contains the instruction set on the left, the data input pins at the top, and the output pins bottom and right sides.

MC6802 Memory

ROM

There’s a 2kBytes (16kb) large ROM on the chip. A NOR type ROM programmed with a masked (depletion) implant.  Comparing this image to a reference I found online and it is clear

(Attribution unsure found in lecture published on-line, original maybe slide set “Digital Integrated Circuits” by Rabaey et al ©2003)

(Static) RAM

 

The 128 Byte (1kb) RAM is also interesting. The datasheet mentions that 32 Bytes of RAM are retainable and this is clearly the smaller section on the left. I can trace the Vcc line of that section to the Vcc/Standby pin. (The larger right side goes to the main Vcc pin.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Counting out the bits, (the small retainable section in one half is 16Bytes or 128bits, so this image contains 4 bits (Or 4 SRAM cells)In part because it is difficult to see the active area and use of buried contacts I cannot figure out the circuit used.  Given this is an NMOS process I suspect it is a resistive load SRAM cell like this one, but I am unable to reverse engineer it from the layout (Without removing the metal).

MC6802 Process

I mentioned buried contacts, or more correctly buried poly contacts.  These are contacts between polysilicon and substrate, used extensively on this part. In a CMOS process you would not find them.  Here is an example of two such contacts on the die

Some commentary about the process quality you can  observe. In 1978 the metal lines would have been wet etched (Likely in a buffered phosphoric acid mixture). Given that the etch quality of the Aluminum tracks appears very good to meYou can see a tiny amount of notching sometimes where the metal line crosses a poly line, and there is slight mis-alignment of metal to contacts, and the metal lines look a little small for the size of the contacts.  But overall though this looks like a good quality process for 1978.

Finally many thanks again to Jeremy for supplying the part, and merry christmas to all of you who celebrate it.

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HCF4007U Dual Complementary Pair plus Inverter

Integrated circuits do not get any simpler than this.  This is an HCF4007 made by ST with a week 27 1993 date code

ST HCF4007UAccording to the datasheet it can be, depending on the pin connections, either 3 inverters, a 3 input NOR or a 3 input NAND gate.

De-capping and you can see it is just 6 transistors! on a 1.47 mm x 1.35 mm die.ST HCF4007U die photo

(click on image for high resolution version)

It is barely an integrated circuit.  Even with my lack of skills I can reverse engineer this part

 

And the pin-out

 

 

 

 

There is one mystery to me.  The part is definitely CMOS as the datasheet specifies it, so  they must be polysilicon gate MOSFETs.  Yet if you look at this high magnification image of a transistor edge, I cannot see the polysilicon??

Thanks to Jeremy for providing the part.

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Arduino CAN Bus Module

Last week I received an early xmas present! A reader, Jeremy kindly sent me a bunch of chips including some truly vintage devices that I will be analyzing over the next few weeks.  Included in the haul was a small CAN Bus controller board for Arduino.  Jeremy was interested in looking at a CAN transceiver chip so I am more than happy to oblige 🙂 CAN (Controller area network) was developed for automotive, and is used in all cars made today. It can communicate between the various ECU’s without the need for a central MCU.  I was not aware that it was being used outside of automotive, I guess with Arduino it is useful as a low cost control bus for home automation type projects.

This is the board containing two chips a timing crystal and four each of capacitors and resistors

 

 

 

The two chips are a Microchip MC2515 CAN bus controller, and the chip we are most interested in, the 8 pin NXP TJA1050 CAN bus transceiver.

 

 

The NXP TJA1050 has a datasheet that indicates it was first launched in 2003. The die is very interesting

(Click on image for high resolution version)

It’s a small die 1.54mm x 1.24mm (1.91 mm2) made on a two metal process. I spend a long time looking at the die trying to figure out what process technology is used. At first I thought it was a CMOS process as there is plenty of polysilicon visible, but the transistors do not look like MOSFETS.  I am now pretty confident that  this part is made on a double polysilicon Bipolar process.  This is a high speed Bipolar process that uses polysilicon to form base contacts and the emitters.  The CAN bus is relatively high speed interface up to 1Mbaud, so it makes sense to use a high speed Bipolar process.

Whilst I am not 100% sure I have it all figured out what layers you can see in the die photo, here is my take on the transistors

I think they have actually used 3 polysilicon layers, first they use an N++ polysilicon that contacts the low resistance collector regions, the second polysilicon is P-type (And the non-silicides regions of this show as pink/purple in my die photo).  This contacts the low doped implanted base doping layer and is a doughnut shape, with a hole that self-aligns the emitter.  The emitter poly (N++) covers the hole and is not directly visible, as it is itself covered with metal (And presumably silicide).

Why I think that three polysilicon layers are used, is that some strange resistor structures are present, that confused me and I can only reconcile with the extra poly.  I am pretty sure the pink layer is p-type polysilicon, but for many resistors like this one, it appears to be sitting on top of another polysilicon layer.  Thus I think they have put the collector polysilicon contact layer under the p-type resistors.  

I do not know why they have done that (Rather than the more conventional placement of resistors over the field oxide). It is possible that these are “pinched resistors” (Resistors where the p-type is used to pinch the n-epi to give a high resistance) but it would be odd to see a chain of pinched resistors, and the resistance value would be huge.

Here is a close-up (Focus stacked) image of another transistor design taken with my 80x objective

This is the block diagram from the datasheet

 

And here is the the pin-out annotated on the die photo

 

 

 

I did manage to trace the CANL and CANH pins to the two 25kΩ resistors, which are the resistors I showed earlier. Which also indicates the pink polysilicon layer has a ~75Ω/sq sheet resistance, to get the 25kΩ resistor value so confirming it is not a pinched resistorI think the driver is the two large transistors that have the part number over them, but I cannot resolve the block diagram to the die photo much further.

Since I de-capped the TJA1050 I also de-capped and took a die photo of the MCP2515 for completeness. It is a modern MCU die, probably made with a 90nm 6 or 8 metal CMOS process, so is not terribly interesting to look at.

Die Size 1.95 mm x 1.66 mm (3,24mm2)

(Click on image for high resolution version)

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