Part quest: USB shell to make tiny dongles - Page 1
Forum section: electronics / general

author: Doofenshmirtz
author_rank: Contributor
timestamp: January 06, 2019, 07:11:05 am
content: The project is a super-small USB dongle - small enough that I want to integrate the USB contacts on the PCB (not use an SMT USB plug). Like this:https://www.gearbest.com/usb-accessories/pp_1700919.htmlBut where to source the rest of the USB plug assembly? Primarily the metal shell, but potentially some of the plastic components, like the sled the PCB sits on (so a special PCB thickness isn't needed).Any pointers to a) what this would be called, and b) manufacturers? Googling things like "usb plug shell" doesn't return useful hits.

author: ebclr
author_rank: Super Contributor
timestamp: January 06, 2019, 10:37:31 pm
content: https://item.taobao.com/item.htm?spm=a230r.1.14.72.6d7a195e66iVRV&id=21106967250&ns=1&abbucket=20#detail

author: TimCambridge
author_rank: Regular Contributor
timestamp: January 07, 2019, 01:21:27 am
content: It looks as if @elbclr has the magic Google-fu. So can I add a related query: Where can I buy the sort of dongle case that's used by the ST-LINK clones and similar.

author: Farley
author_rank: Regular Contributor
timestamp: January 07, 2019, 02:22:33 am
content: Google the phrase "usb dongle enclosure"

author: Doofenshmirtz
author_rank: Contributor
timestamp: January 07, 2019, 05:41:28 am
content: Thanks for the pointer, but my description here must be as bad as my Google-fu... that's not the portion I'm after.It seems there are roughly 4 parts to a tiny dongle assembly:PCB with the contacts and SMTMetal shell / shieldRear plastic capA plastic carrier for the PCB that adds thickness and a bumper at the front of the plug where the wipers strike. This might be part of the rear cap mold.While I'd love to find a "just add your PCB" kit, I'd settle for finding the metal shell. (We may need to do our own plastics anyway.)Thanks!

author: beanflying
author_rank: Super Contributor
timestamp: January 07, 2019, 06:00:22 am
content: Depending on your quantity and IF you are likely to ever want to service the internals after manufacture, sealing the board into the enclosure makes sense for ruggedness.Consider RIM (Rapid Injection Molding) one of it's benefits is much lower temperatures than conventional Injection molding it also allows the use of composite tooling which is far cheaper than metal needed for IM. The Board would be placed into the tool then have the plastic shot around it. You should be able to run over this option with a car.If you only want very small prototype (maybe sub 100) lots then 3D Printing with FDM is cheap and easy or if you want a fine finish look at Resin based options. Most likely would need to be made in two halves then fused or glued together.There are some USB cases I have got from Aliexpress or E14 (farnells) but they were always a compromise and looked cludgey.

author: Doofenshmirtz
author_rank: Contributor
timestamp: January 07, 2019, 06:51:28 am
content: Quote from: beanflying on January 07, 2019, 06:00:22 amYep, even for small proto runs, injection molding is within grasp for us, and thermal expansion differences are probably not a hazard at this scale. (Small-shot machine and ready access to a CNC machine shop. Form1 even has an SLA resin that'll tolerate about 100 shots, so you can SLA print your injection mold.)It's the pesky metal shell that's the gap. Trying to stamp and form that would just be stupid.

author: beanflying
author_rank: Super Contributor
timestamp: January 07, 2019, 07:08:09 am
content: I haven't looked at buying an SLA printer as I might go weeks without running it so clean up mess and waste would be a pain. Interesting on a tooling grade resin however should I ever need to look at it.I have a good mate who is a pattern maker that does a heap of RIM tooling for short run production for the custom Auto industry in particular (generally 500/year sort of thing). They were shooting whole plastic front bumper assemblies in a single resin tool was about the biggest mold I have seen them do. As it is a much less heat intense process you should be able to fully encapsulate good sized boards using it leaving wires or plugs poking out as needed.Any particular reason to add a metal shell? Shielding or similar?

author: beanflying
author_rank: Super Contributor
timestamp: January 07, 2019, 07:30:55 am
content: Maybe have a browse of E14's range too. You may find one you like.https://au.element14.com/c/enclosures-racks-cabinets/enclosures-boxes-cases/prl/results?enclosure-type=usb

author: JVR
author_rank: Regular Contributor
timestamp: January 07, 2019, 11:19:06 am
content: If you are making volume, any of the big brand manufacturers will talk to you, to either sell you bits, or help you make the connector using your own PCB. If this is not a volume product, is it worth the hassle to save the 3mm that a stock USB connector needs to function?

author: Doofenshmirtz
author_rank: Contributor
timestamp: January 07, 2019, 03:38:06 pm
content: Anything's possible with volume, no? ;-) We're looking at 100's to low 1000's in volume, so no larger manufacturer will bother (or the cost would be prohibitive). I expect we need to find the part through distribution. We're looking to use a turnkey dongle to start, so there's a prospect of asking that vendor to collaborate on the customized version. Using a discrete connector isn't a deal-breaker, but it's a significant design minus.Why the metal shell? It's part of a commercial offering, and being installed long-term in a transportation environment (vibration), so the extra mechanical structure would be useful to keep the dongle seated. Ordering a thicker PCB wouldn't be a deal-breaker, but it seems less suitable. I suppose we could explore molding it in plastic as part of the body, but I haven't seen anyone do this before so I'm hesitant.SLA injection mold... yep, the idea is to make an aluminum mold shell to handle the process stress, with a cavity to drop in an SLA-printed insert. It's a clever balance for speed and cost for small-ish runs where SLA-grade resolution is acceptable, and for testing designs before committing to molds. The SLA mold resin is resistant to high temperatures, and they claim a life of around 100 shots per print.Direct encapsulation... the problem with thermal expansion is two-fold, from my reading - first, shrinkage of the plastic during curing; also, thermal cycling where the plastic, FR4, and components have different coefficients; both can mechanically stress solder joints. At this tiny size, I don't think this is a problem, and servicing the board isn't needed. If we could source the metal shell, we probably would directly mold the body around it.

author: Gribo
author_rank: Frequent Contributor
timestamp: January 08, 2019, 02:11:48 pm
content: Doe this fit the bill?https://www.aliexpress.com/item/5-sets-DIY-USB-2-0-A-type-Male-Connector-Assembly-Adapter-Plug-Socket-Metal-shell/32798192247.html

author: Doofenshmirtz
author_rank: Contributor
timestamp: January 08, 2019, 05:25:03 pm
content: Yep, the top part is similar to what I'm after.

author: langwadt
author_rank: Super Contributor
timestamp: January 08, 2019, 05:49:48 pm
content: keep in mind that the usual ENIG gold is probably borderline for an edge connector, it should ideally be hard plated gold

author: Doofenshmirtz
author_rank: Contributor
timestamp: January 08, 2019, 09:02:14 pm
content: Quote from: langwadt on January 08, 2019, 05:49:48 pmUnderstood. For this application, we don't need 5000+ insertion cycles. 100 would do the trick. (It's an insert-once-and-leave-it device.)

author: janekm
author_rank: Unknown
timestamp: January 08, 2019, 10:31:54 pm
content: Try talking to this shop, they seem to have what you are after if I understood it right: 【金属U盘外壳U盘配件 装短黑胶体外壳 DIY定制 短版黑胶体U盘外壳】https://m.tb.cn/h.3Iq5JXK?sm=c5bfd3 点击链接，再选择浏览器咑閞；或復·制这段描述￥5Rcqbq8x0Lg￥后到👉淘♂寳♀👈Alternatively find a factory on Alibaba that makes custom USB flash drives, they will have access to many variants of shells.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 10, 2019, 03:05:20 pm
content: Technomelt from Henkel. You can make moulds in aluminium. Its low set point ( about 180C ) and very low pressure make it suitable for encapsulation. Its tough as boots.