Help me replace a QFP100 MCU with another MCU mounted on an interposer PCB - Page 1
Forum section: electronics / projects

author: DC1MC
author_rank: Super Contributor
timestamp: May 08, 2020, 10:58:06 pm
content: 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.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,DC1MCEDIT: Replaced QFN with QFP

author: langwadt
author_rank: Super Contributor
timestamp: May 08, 2020, 11:11:56 pm
content: is it really QFN and not QFP?

author: DC1MC
author_rank: Super Contributor
timestamp: May 08, 2020, 11:26:42 pm
content: Quote from: langwadt on May 08, 2020, 11:11:56 pmSorry, of course is a QFP, it has pins, brain fartJEITA calls it P-TQFP100-14x14-0.50 and Hitachi code was TFP-100BThe pdf is here:https://datasheetspdf.com/pdf/660702/RenesasTechnology/HD6432345/1and the footprint at page 921Thanks for pointing this out,DC1MC

author: Ian.M
author_rank: Super Contributor
timestamp: May 09, 2020, 12:15:02 am
content: 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.

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 10:20:47 am
content: Quote from: Ian.M on May 09, 2020, 12:15:02 amWell, 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,DC1MCEDIT: 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.

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 11:12:33 am
content: OK, must use another plan, got the name and the technology, but the minimum pitch available for mortal is 1,15mmJust in case someone will ever need something similar, here is the link to some plated half-holes:https://www.multi-circuit-boards.eu/en/pcb-design-aid/drills-throughplating/plated-half-holes.htmlCheers,DC1MC

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 09, 2020, 11:53:12 am
content: More likely you could look for connectors with that pin pitch, and see if there's one with the pins exposed such they can be soldered to two boards at once?Making it as a no-lead would be feasible in that you can make pads on the face of the PCB, of course; but good luck inspecting that, plus you have to solder through the board, which isn't very conductive, so you'll probably terribly overheat everything on top, and need a very high temp laminate as well. (Ceramic PCB would be very attractive, but sheesh, good luck with that? I mean, prototypes are available economically these days, but not like home-hacker economical I don't think.)Tim

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 12:26:36 pm
content: Quote from: T3sl4co1l on May 09, 2020, 11:53:12 amIf that would have been some kind of dip package the connector idea would have worked, but is a QFP, my idea was if here was a possibility to do something like a "dice cut" QFN PCB to place it instead of the original package and on that pcb to place a BGA MCU. Sorry, I'm unfortunately not familiat with the PCB industry jargon to describe this better.I could solder with a micropencil the pseudo-QFN PCB, I've did it with real QFN with that pitch, it was painful without a microscope, but I'm not doing mass-production here and I plan to get a proper microscope.But as far as I could find, the only way to have a bit of higher PCB side contacts, for reliable soldering, is to use either half vias or ceramic stuff, half vias have a too big pitch and ceramic will cost more than the transceivers I want to repair. Otherwise nobody will deposit copper on the sides to create the pseudo-pads, or at least I didn't find any.Now I'm wondering if a QFP on QFP footprint PCB can be soldered with some degree of success by a "normal" person, without destroying anything, even in principle. That is either micro-pencil or hot air.Cheers,DC1MC

author: JDubU
author_rank: Frequent Contributor
timestamp: May 09, 2020, 01:53:06 pm
content: Quote from: DC1MC on May 08, 2020, 10:58:06 pmAre you sure that HD6432345A20FA is the part number of the failed MCU?The Hitachi data sheet (page 893) shows this to be a mask ROM version:Appendix F Product Code LineupTable F.1 H8S/2345 Series Product Code LineupProduct Type Product Code Mark Code Package (Hitachi Package Code)H8S/2345 Mask ROM HD6432345 HD6432345(***)TE 100-pin TQFP (TFP-100B)HD6432345(***)TF 100-pin TQFP (TFP-100G)*HD6432345(***)F 100-pin QFP (FP-100A)HD6432345(***)FA 100-pin QFP (FP-100B)]ZTAT™ HD6472345 HD6472345TE 100-pin TQFP (TFP-100B)HD6472345TF 100-pin TQFP (TFP-100G)*HD6472345F 100-pin QFP (FP-100A)HD6472345FA 100-pin QFP (FP-100B)F-ZTAT™ HD64F2345 HD64F2345TE 100-pin TQFP (TFP-100B)HD64F2345TF 100-pin TQFP (TFP-100G)*HD64F2345F 100-pin QFP (FP-100A)HD64F2345FA 100-pin QFP (FP-100B)...Note: (***) indicates the ROM code.Are you saying that you are planning to rewrite all of this MCU's firmware and replace the part with a flash version?

author: mikerj
author_rank: Super Contributor
timestamp: May 09, 2020, 02:11:13 pm
content: Something that could probably work for you are the QFP solder base adapters that are used for connecting things like emulators to PCBs e.g. likethis Ceibo part. Note that these tend to be fairly niche/low volume parts so don't expect low cost.

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 03:24:27 pm
content: @JDubU I've verified, I have the flash version on both units, that doesn't matter if they are replaced, what matters is that one unit is still accessible via serial port and if I could get compatible replacement chips I intend to read and transfer the firmware.Original idea was to replace the crappy MCU with an STM32F or similar and then indeed write the fw from scratch, is actually not such a big deal to drive a parallel LCD and a couple of encoders and switches. Was a big deal in the '90s, when the tools were pretty spartan, but not nowadays. As the last resort I will hook at the data cable a Nucleo 767ZI and use it to drive the RF part, it will loose any portability, but still better than scrap them.A nice Italian parts seller is asking for 130EUR per whole front panel, or so he says, not a bad price if you want to recover a 14yr old radio, but not worth spending if they don't take the the damaged one for refurbishing to offset the cost.Cheers,DC1MC

author: Ian.M
author_rank: Super Contributor
timestamp: May 09, 2020, 03:44:10 pm
content: 0.5 mm pitch is viable as a BGA, and you can get low temperature alloy BGA solder balls, normally used for reballing. It therefore should be possible to make a transposer board with a QFN footprint top-side and on the bottom side 0.5mm pitch pads just inside its perimeter, sized to land on the inner end of the existing QFP pads. Depending on the decoupling requirements and the difference between the transposer board size and the QFN MCU footprint you may not have room for top-side decoupling where you need them so may need to resort to decoupling within the interposer thickness which could be done with a two PCB interposer, with the lower one a narrow frame with its center milled out to clear caps on the underside of the upper one. Assemble the interposer by normal reflow using standard solder paste, ball it with low temperature balls and reflow it onto the front panel board's QFP footprint. The combination of low temperature balls, and the QFP pads extending past the interposer edge should make it reflowable without cooking it or even melting the standard temperature solder it was assembled with..However developing and debugging the interposer design and practising its assembly and final reflow is a *LOT* of work + significant expense for the multilayer interposer. The interposer is probably tougher to design and construct than a complete front panel board replacement, + salvaging and refitting the existing controls and displays. If you are scared of that, the interposer idea is almost certainly non-viable for you.Dead bugging is *<EXPLETIVE>* tedious, but with decent magnification, a steady hand and working methodically, has an excellent chance of success. Its also minimum risk as you'd have to be really unlucky and ham-handed to lift pads on the existing footprint. IMHO lay off the caffeine for 24H, plan it out, and sit down at the bench and have a go at dead bugging it, with a checklist of connections sorted in order from shortest to longest, and continuity checking them as you go and again on completion.

author: JDubU
author_rank: Frequent Contributor
timestamp: May 09, 2020, 03:58:01 pm
content: Quote from: DC1MC on May 09, 2020, 03:24:27 pmDon't know if this company is legitimate:http://www.odysseyelectronics.net/ps.htmhttp://www.odysseyelectronics.net/results.html?part=HD6432345FA+&Submit1=Start+Search&search_db=true&user=odyssey

author: langwadt
author_rank: Super Contributor
timestamp: May 09, 2020, 04:24:26 pm
content: if there is enough space around the part maybe some 0.5mm pitch FFC connectors and flex cables to a board with a different MCU

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 05:29:27 pm
content: Just in case someone want to assist me redesigning the board or for other ideas, here are a couple of pictures just to see the size and situation, I can reliably say that every important component (sockets, LCD and so on ) is recoverable, also many MCU traces have vias that may help with connecting some wires, there are something like 30 or so unaccounted

author: JDubU
author_rank: Frequent Contributor
timestamp: May 09, 2020, 06:31:52 pm
content: Here's a possible source:https://m.alibaba.com/amp/product/62358723017.html

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 06:49:50 pm
content: 29USD per piece is not that bad, do you know anything about that seller, or was just a search result ?In any case, many thanks, I'll try to read the original fw and if I succeed is the less hassle way, assuming that I don't get some defective of remarked fakes.Cheers,DC1MC

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 09, 2020, 07:34:57 pm
content: Would it not be more reasonable to trace the PCB it's on?Tim

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 07:40:57 pm
content: Quote from: T3sl4co1l on May 09, 2020, 07:34:57 pmSorry Tim, I think I've hit a language barrier, do you care to explain what you wanted to say a bit more in detail ?DC1MC

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 09, 2020, 07:41:54 pm
content: Trace the PCB's circuit, reverse-engineer and replicate it whole? With substitutions for available parts of course.Tim

author: DC1MC
author_rank: Super Contributor
timestamp: May 09, 2020, 08:01:33 pm
content: Quote from: T3sl4co1l on May 09, 2020, 07:41:54 pmThis it maybe easy for somebody that does this for a living or as a hobby, I didn't know where to start and what program to use to produce some usable gerbers for production. Of course I can measure the board shape and size and position position of fixed components (encoders, LCD, connectors and so on). Putting this in a schematic capture / layout program is sadly beyond my abilities currently, what little AD I knew I've forgotten by not using it in the last 10yrs or so, and Kicad is fully alien to me.There are also some analogue bypass things that don't interact with the MCU (volume potentiometer and so on).As the schematic with the new MCU will suffer significant modifications, I'm not sure if other than placing the fixed position parts will bring me, I need somebody that can really do layouting and did a few successful production runs as well, but unfortunately thisiis not the most interesting project and I'm not rich. In the end, assuming that the Italian seller is legit I can get one replacement assembly per month for 130+17EUR shipping, I was thinking to do something either very cheap or that I will lern form it.

author: JDubU
author_rank: Frequent Contributor
timestamp: May 09, 2020, 09:02:55 pm
content: Quote from: DC1MC on May 09, 2020, 06:49:50 pmJust a search result.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 09, 2020, 10:56:04 pm
content: Well, what were you planning on doing anyway? An interposer needs to bedesigned, and it's probably going to need a schematic and layout for that. So will the rest of the board. Sounds like a learning opportunity either way.Tim

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: May 09, 2020, 11:21:33 pm
content: I'd think it's easier to redesign the board to use a different display altogether of similar size (there are a lot of small OLED and TFT panels of similar size), make it match the dimensions of the existing PCB.

author: Miti
author_rank: Super Contributor
timestamp: May 09, 2020, 11:24:01 pm
content: TheQuote from: DC1MC on May 09, 2020, 10:20:47 amThose are castelated holes or castelated pins. PCBWay offers that option but you can't make it that dense.My advice, buy it from the Italian and try a different project for learning PCB design.