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Help me replace a QFP100 MCU with another MCU mounted on an interposer PCB
DC1MC:
Hello dear experts in pcb design, I have a (relatively) strange question and maybe you can help me suggesting a solution.
I have a pair of HAM transceivers (YAESU FT-817ND) that have a defective front panel MCU, the MCU is nothing special except that is a Hitachi, nee NEC, nee Renesas unobtanium obsolete chip in a QFP100 package and the PCB assembly doesn't make sense to be replaced, because Yaesu charges for parts with a price policy similar to Apple |O.
One of the two possible options to deal with that is to replace the chip with another MCU with similar or better features and rewrite the firmware to control the LCD, a couple of encoders and switches and a few leds.
The right option will be of course to replace the PCB with a newly designed one, but this is a bit too much for me and I have this idea of making some kind of interposer pcb with side contacts that will hold the new MCU.
The problem is that the original QFP100 has 0.5mm pitch and while I have seen hybrids with side contacts for surface mounting I've never seen with such a small pitch .
So my question is: is this a feasible way to replace the MCU, are there any other solutions that can be implemented with a reasonable cost, like a soldered flex cable, any ideas are most welcome, including a reliable source of reasonably priced HD6432345A20FA (aka H8S/2345). Because plan B is to just hijack the flex cable to the main-unit and make some kind of kludge just to control the radio part with a PC program.
Thanks,
DC1MC
EDIT: Replaced QFN with QFP
langwadt:
is it really QFN and not QFP?
DC1MC:
--- Quote from: langwadt on May 08, 2020, 11:11:56 pm ---is it really QFN and not QFP?
--- End quote ---
Sorry, of course is a QFP, it has pins, brain fart :palm: JEITA calls it P-TQFP100-14x14-0.50 and Hitachi code was TFP-100B
The pdf is here: https://datasheetspdf.com/pdf/660702/RenesasTechnology/HD6432345/1 and the footprint at page 921 :rant:
Thanks for pointing this out,
DC1MC
Ian.M:
If there's a suitable QFN MCU that will fit within the footprint, 'dead bug' it with any decoupling caps required soldered to the new MCU's central exposed pad to minimise the wire length to Vcc pins, tie all grounds to the exposed pad, and jumper over from the new QFN's pin pads to the QFP footprint pads on the board with fine magnet wire scrambling the pinout as required. If there isn't an ICSP header on the board you can reuse, hook one up direct to the QFN on a trailing fly-lead.
DC1MC:
--- Quote from: Ian.M on May 09, 2020, 12:15:02 am ---If there's a suitable QFN MCU that will fit within the footprint, 'dead bug' it with any decoupling caps required soldered to the new MCU's central exposed pad to minimise the wire length to Vcc pins, tie all grounds to the exposed pad, and jumper over from the new QFN's pin pads to the QFP footprint pads on the board with fine magnet wire scrambling the pinout as required. If there isn't an ICSP header on the board you can reuse, hook one up direct to the QFN on a trailing fly-lead.
--- End quote ---
Well, the "dead bug" thing is what I want to avoid, soldering tens of 0.2mm criss-crossed wires wires is not for the weak willed, this is why I was asking if someone has experience with the side contacts PCBs that I could solder with less pain or something else besides this.
Cheers,
DC1MC
EDIT: Just to illustrate what I mean, I've added a picture of one of my PCBs with a hybrid module soldered on, it is exactly what I want to have, and I wonder how this technology is called and if a 0.5mm is feasible.
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