How to solder DIP onto SMD footprint on a commercial PCB. - Page 1
Forum section: electronics / projects

author: johm
author_rank: Contributor
timestamp: June 27, 2017, 01:19:53 pm
content: The world is flooded with SMD to DIP adapters, but I'd like to solder a custom DIP PIC microcontroller (14 pin) onto an existing unpopulated SOIC footprint (14 pin) in a PCB. The pins don't match at all, so I'd need to rerout each pin. Any ideas on how to approach this without having to build/order a new PCB?Apologies for the weirdness or how stupid this may sound.Johm

author: MosherIV
author_rank: Super Contributor
timestamp: June 27, 2017, 01:23:15 pm
content: Make your own permanent adapter board with strip board, 14 pin IC socket.Mount this strip board somewhere on the PCB and hand wire each pin to the PCB.Ugly but i works

author: bktemp
author_rank: Super Contributor
timestamp: June 27, 2017, 01:31:46 pm
content: If you have the firmware, the best solution is to use the PIC with the correct package (most PICs are available in SOIC).If it is a one-off solution, mount the PIC somewhere on the board and connect each pin individually to the SOIC footprint.If it needs to be more ruggedized, make a small PCB with castellated vias matching the SOIC footprint and a small SMD connector in the middle, connecting to an external PCB holding the DIP IC using a short FFC or some other high density cable.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 02:25:16 pm
content: Microchip used to sell transition socket adapters that allowed their DIP footprint ICD/ICE processor emulation headers to be used on SMD footprints. They discontinued them but the OEM suppliers and their competitors still make many of them or equivalents. The only ones you'll have problems with finding off-the-shelf is when the DIP and SMD package have different pin counts.Winslow W9534P 14pin DIP to SOIC/SOJ(available from R.S. Components as 240-6595 ) - not cheap but better than paying salary and overheads for a tech to futz around for an hour with a DIP socket, magnet wire and epoxy putty.For SOIC-8-N, SOIC-14-N and SOIC-20-N you can probably bodge together a cheaper equivalent with a pair of dual row SMD 0.127mm pitch male and female headers, a bare SOIC to DIP adapter PCB flipped SOIC side down and a DIP socket. You are going to have to do some digging through connector manufacturers datasheets to find a pair of headers that will fit on a SOIC-N footprint and it depends how much extra pad length you've got.The 18 pin PIC PDIP footprint doesn't have a 1:1 mapping to a SOIC footprint. Those PICs use a SOIC-20-N package with the Vdd and Vss pins (in the middle of each side) doubled up, so you need a custom adapter PCB.

author: alm
author_rank: Super Contributor
timestamp: June 27, 2017, 02:32:33 pm
content: What I have used in the past to connect to SOIC footprints is to solder a 50 mil surface mount pin header (likethis) to the footprint. You can then connect a suitable ribbon cable or even tiny PCB to it.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 27, 2017, 03:25:23 pm
content: You could dead-bug it. Flip the DIP upside down and glue it in place, then air-wire the pins where they need to go.

author: Fungus
author_rank: Super Contributor
timestamp: June 27, 2017, 03:52:59 pm
content: Like this, but flipped over...

author: Fungus
author_rank: Super Contributor
timestamp: June 27, 2017, 03:56:22 pm
content: Difficulty level: 11

author: MosherIV
author_rank: Super Contributor
timestamp: June 27, 2017, 04:03:34 pm
content: QuoteUnless I am mistaken, I think the OP want it the other way around - how to solder a DIL to SOIC

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 04:45:32 pm
content: You can still do it that way - solder magnet wire to all the pads of the SOIC footprint and fan the wires outwards, bend out the pins of a DIP socket for easy access, glue an insulating spacer to the footprint with the socket glued on top and then solder each individual wire to the corresponding bent out pin and reinforce the sides with epoxy putty or hot glue. However that is for sure going to involve 'futzing around for an hour' and is uneconomic unless you are a hobbyist or are on too tight a deadline to get the commercial adapter overnighted to you.A preferable less fiddly method if you can stand longer wires is to crop the pins on a turned pin socket so they are significantly shorter than Veroboard thickness, and use a scrap of Veroboard with the socket solderd to the copper side as a breakout board for the socket. It can then be glued down anywhere convenient and patch wired pin by pin to the SOIC footprint.

author: KL27x
author_rank: Super Contributor
timestamp: June 27, 2017, 06:11:55 pm
content: re Fungus pic: I hope it worked.I suppose impedance matching was important. Otherwise, I imagine it would be a lot easier to have done that dead bug.

author: KL27x
author_rank: Super Contributor
timestamp: June 27, 2017, 06:22:13 pm
content: OP, Generally all I would do is glue the chip down next to the footprint with hot snot. Then make the connections with 30AWG kynar wire. Nothin' to it but to do it.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 06:37:51 pm
content: Quote from: KL27x on June 27, 2017, 06:22:13 pmYes - upside down 'dead bug' style, but that makes it impossible to swap the chip without major rework, hence my recommendation to use a scrap of veroboard copper side up as a breakout board for a turned pin socket with the pins cropped so they don't short to the underlying main PCB.

author: KL27x
author_rank: Super Contributor
timestamp: June 27, 2017, 06:48:03 pm
content: ^Yeah, that is a good idea if you want to swap the chip.If that doesn't matter, and I were going to glue the chip, I wouldn't do it deadbug. I'd bend the pins out and clip them (or bend them up if you want to use wire wrap) and glue the chip "live bug." There's no reason to read the pinout upside down, in this case.If the pinout matched, yeah, I'd go dead bug, then it would be easier to route the wires. Stitch up the close row, straight across. Then stitch up the outer row, over the top.

author: Fungus
author_rank: Super Contributor
timestamp: June 27, 2017, 07:02:24 pm
content: Quote from: MosherIV on June 27, 2017, 04:03:34 pmHence the "flipped"(I mean, notexactlylike that, but it's the only image I could find. I'm sure you get the concept though).Me? I'd solder a bunch of wires to the legs of a DIP socket, insert the chip, trim wires to length, bend them to right angle, solder them to the PCB.(and hope I never need to change the chip)Quote from: KL27x on June 27, 2017, 06:11:55 pmIt wasn't me! It turned up when I searched for a suitable image.

author: alm
author_rank: Super Contributor
timestamp: June 27, 2017, 07:28:06 pm
content: Attached is a picture of the connector solution I used. Much faster and neater than messing around with 30 awg wire in my opinion.

author: KL27x
author_rank: Super Contributor
timestamp: June 27, 2017, 08:09:28 pm
content: That is slick as snot. I wonder if wire wrap tool fits in that tight a pitch?

author: DaJMasta
author_rank: Super Contributor
timestamp: June 27, 2017, 08:13:04 pm
content: Probably not, looks like a 0.05" header, but it's a standard size so you can get a connecting adapter which would mean you can do all your rewiring off board and then plug it in, which is nice. I don't think the connector plastic is durable enough, but you could potentially even bend a few pins out to directly touch the DIP pins.

author: alm
author_rank: Super Contributor
timestamp: June 27, 2017, 08:19:15 pm
content: Yep, that is the 50 mil header I posted the part number of. I am not aware of wire wrap sockets with pitch less than 100 mil, so I would not expect any standard wire-wrap tool to fit. As for bending, I have never tried that. I doubt the pins are even long enough for that: to go from 7 pins at 50 mil to 7 pins at 100 mil, your pins would have to extend about 4.5 mm on each side. Never mind the extra width of a DIP package. I have only used it with either a 50 mil IDC connector or a female connector soldered to a tiny adapter board. Obviously you do not want something heavy hanging off those surface mount pads if vibration is an issue.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 08:40:14 pm
content: If vibration or shock is an issue, you are better off dead-bugging the chip or bonding on a breakout board and patch-wiring it. However if you *REALLY* *NEED* that SMD header, lightly abrade the pcb round the footprint and the plastic body of the header with a fibreglass pencil to key the surfaces for gluing, thoroughly clean and deflux the board after soldering, dry with hot air and apply epoxy round it up to the top of the plastic base while the board is still warm. If you squegee the epoxy in from one side till it comes out the other you can get it to fill most of the voids under the header base and with enough fillet area, once set the pins will break before the header and blob of epoxy peel from the board.

author: tooki
author_rank: Super Contributor
timestamp: June 27, 2017, 08:50:47 pm
content: Quote from: Fungus on June 27, 2017, 03:56:22 pmSweet jesus. Any back story on that?

author: KL27x
author_rank: Super Contributor
timestamp: June 27, 2017, 09:41:34 pm
content: QuoteAhh... So far, I have not loved a PCB so much to want to make a custom adapter board where kynar wire and a lot of squinting will do. (With a stereomicroscope, this is actually just business as usual). But this is great to know for the rare occasion.

author: johm
author_rank: Contributor
timestamp: June 27, 2017, 09:58:22 pm
content: Thx for your answers :-Dalm's solution seemed really appealing, but I cannot afford waiting for new components to arrive (I don't have headers different than 100mil pitch), so I'm currently at work on dead-bugging (is that a verb?) my poor PIC16F1455 and with some 30AWG wire, rerout them to the correct SMD pads, a bit messy...

author: johm
author_rank: Contributor
timestamp: June 27, 2017, 10:38:22 pm
content: For those interested, all this hassle was because I couldn't find which microntroller they had on a magnetic card reader.It is a cheap one I bought off ebay for 10USD but that can't read custom card protocols. I dissasembled it and found an ST064C opamp that does some crude analog signal processing and a chinese microcontroller. The pinout is really weird, can't find a direct replacement (yes, it's a *16 pin SOIC: I can't count). Neither microchip nor microchip(atmel) have 16pin microcontrollers. So I decided to reinvent the card decoding wheel on my PIC16F1455. Now my firmware on the PIC directly reads and decodes the custom card encoding and transmits to the PC via a HID interface.Hence my want to solder a dip PIC onto a SOIC footprint.EDIT: The existing chinese micro is going to be surreptitiously unpopulated.

author: KL27x
author_rank: Super Contributor
timestamp: June 27, 2017, 10:46:43 pm
content: Well, this is probably beyond obvious to anyone who has even done it. But just in case...You can catch some of your traces to the nice fat blobs on some of those caps and/or other surrounding areas.Also, if you like to keep things tidy, what I oft do is to glue a bit of copper clad (I got the 0.007" thick 1/2 oz pour FR4 for things like this) to the top of the IC (or bottom, if it's "dead") for the decoupling cap and/or other small bits of circuitry. I just use a battery powered engraving tool to cut the copper. Place it where you can catch the power/ground pins and the pcb track with the end of the same jumper, or you can even fold over a DIP pin and solder it to the end of the cap.Since switching over to SMD parts, I use this quite often when breadboarding with DIP IC's. There is an ocean of space on top these IC's. 0603 resistors and caps and diodes galore can fit on there.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 11:16:37 pm
content: The only good option there is to dead bug it. As it only appears to use eight I/O pins (excluding USB) you should be able to reserve the PIC ICSP pins so you can patch in an ICSP/ICD header on a short flylead if you need to upgrade or debug your firmware. If it needed more pins, I'd suggest the 20 pin PIC16F1459.I'd suggest using the QFN package part rather than PDIP as, assuming you've got good eyesight and steady hands, its easier to dead-bug neatly and robustly - glue it down pads up just above the green wire and you wont have far to run the patch wires. Don't forget to mark pin 1 on the underside *BEFORE* gluing! SOIC is also possible, but PDIP is excessively big and clumsy.

author: KL27x
author_rank: Super Contributor
timestamp: June 27, 2017, 11:39:04 pm
content: QuoteThe PIC micros I use all have a corner cut out of the center/thermal pad to denote pin 1.

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 11:51:17 pm
content: There's still the possibility of massive confusion due to mental failure to mirror the pinout because the chip's got its arse in the air!Physically marking the bottom of the chip right next to pin 1 helps prevent that sort of brain-fart, by giving you a hint to start counting round the pins in the right direction.