Very small and thin transparent enclosure - Page 1
Forum section: electronics / projects

author: jmaja
author_rank: Frequent Contributor
timestamp: February 05, 2019, 06:21:35 pm
content: Where can I find an enclosure for a prototype/small number product with the following specifications?-Needs to be transparent or at least have windows for several LEDs and sensors (IR and visible).-Needs to be very thin. The PCB+components will be 4 mm. Thickness is critical, thus hoping to find 6 mm etc. outside height.-Size could be 30x40, 40x50, 30x80, 20x80 mm or something similar.It would also help, if the case is water tight and can be opened for battery replacement.

author: ebastler
author_rank: Super Contributor
timestamp: February 05, 2019, 06:33:58 pm
content: Something like this, maybe?https://ace-cases.com/product/compactflash-cf-case-for-single-cf-cardsmart-memory-media/Similar cases for SD-Cards are also available, but may be too small.None of them are water-tight, I'm afraid.

author: Ian.M
author_rank: Super Contributor
timestamp: February 05, 2019, 06:49:38 pm
content: Short of milling a case out of aluminum bar stock with a raised rim to protect the edges of a clear acrylic or polycarbonate sheet lid, with an O ring groove for a seal and a line of tapped holes outside the O ring groove to screw down the lid, I think that's going to be very difficult in small quantities. Even so, 6mm thick is unrealistic - you might manage 7mm - as IMHO 1mm is too thin for a plastic lid that needs to be both removable and make a watertight seal, especially if its got to have countersunk screws through it.

author: Nusa
author_rank: Super Contributor
timestamp: February 05, 2019, 07:12:34 pm
content: Clear shrink-wrap tubing. Cut long and seal ends with glue if you want water protection.For battery replacement, cut it off and use a new piece of tube.

author: jmaja
author_rank: Frequent Contributor
timestamp: February 05, 2019, 07:43:00 pm
content: One thing I forgot to mention was that there must be a way to fix this enclosure to a surface. E.g. a two holes for webbing etc.Could heat shrink tube really work for this? I could put the fixing wholes to the PCB. Or use the extra heat shrink tube for fixing. Would it seal well enough against the PCB or itself. I haven't used that big heat shrink tubes before.Would the glue still be transparent?Battery replacement is not a must and could be done with a heat shrink. The battery should last several years, which may be as long as the useful life anyway.The product will not be submerged, but will be outdoors in a rain.One idea I just got from polycarbonate. Maybe it could be feasible to to use 1 mm and 4 mm polycarboate? Cut a rim out of 4 mm and the glue or fuse the 1 mm top and bottom to it.https://www.cutplasticsheeting.co.uk/blog/uncategorized/how-to-glue-polycarbonate/Can't be opened and closed, but would be rather strong and easy to mill.

author: ebastler
author_rank: Super Contributor
timestamp: February 05, 2019, 08:04:59 pm
content: I think it's time for you to tell us about your actual use case. It's a bit frustrating to make a proposal and then just hear back "Ah, and it needs to do this too"...If it attaches to atablelarger object, why does it have to be so thin? And attaching with webbing??

author: jmaja
author_rank: Frequent Contributor
timestamp: February 05, 2019, 08:13:53 pm
content: It will be attached to a canvas outdoors. It can't stick out much from the canvas.

author: ebastler
author_rank: Super Contributor
timestamp: February 05, 2019, 08:16:33 pm
content: Quote from: jmaja on February 05, 2019, 08:13:53 pmSo the actual use is a trade secret, since it will make you rich.Fine, but I am no longer interested in guessing games. Maybe others are.

author: jmaja
author_rank: Frequent Contributor
timestamp: February 05, 2019, 08:29:07 pm
content: Quote from: ebastler on February 05, 2019, 08:16:33 pmCertainly will not make me rich. If I thought it would, I would order a custom enclosure from some manufacturer. Since I don't see making many of these, I don't want to spend a lot of money on the enclosure.But sorry I don't feel comfortable revealing the application.

author: Nusa
author_rank: Super Contributor
timestamp: February 05, 2019, 08:53:14 pm
content: You'll have to do some experimenting to determine what's suitable, especially if you need abrasion resistance as well, which being attached to canvas implies. Direct sunlight will degrade most unpainted plastics in a couple years...I know generic tie-wraps used outdoors don't last much longer than that.My only other thought is embedding your device in epoxy resin. The learning curve on that will be higher, unless you find someone who already knows how it's done. Here's a page that might get you started:https://hackaday.io/project/21914-resin-in-resin

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2019, 11:40:51 pm
content: Quote from: ebastler on February 05, 2019, 08:04:59 pmsometime sthis forum makes you feel like a unpaid kinda voluntary product designer huh

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 05, 2019, 11:58:39 pm
content: Thin, transparent, water-tight, can be opened (I guess "easily")... yeah. Almost Santa's list.Maybe recycle old (or not) watch housings? You can find them water tight, with a nice transparent window, and they can be opened. A typical watch may not be large enough I guess..., but that's worth a look?

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: February 06, 2019, 02:20:26 am
content: You could do it easily with a 3D printer.1mm thickness is fine. Using flexible material, you probably can have a water tight lid. No problem to add some pads with hole to screw it to something.

author: Ian.M
author_rank: Super Contributor
timestamp: February 06, 2019, 02:49:53 am
content: 3D print something or laser cut polycarbonate and glue it up like a layer cake, and you'll be replacing the enclosures annually due to UV degradation. Painting them opaque black and you'll cure that but then the optical and IR sensors wont work.Since its a prototype, why not solder them up out of brass shim stock, with epoxied in mica windows for the sensors? Tin the whole exterior for better corrosion resistance. You wont be able to make the battery easily replaceable without desoldering the cover.Quote from: jmaja on February 05, 2019, 08:13:53 pmQuote from: jmaja on February 05, 2019, 08:29:07 pmSo, you want to cam bug the toilet tent at a festival?

author: daniel444
author_rank: Regular Contributor
timestamp: February 06, 2019, 03:54:13 am
content: just buy an off the shelf aluminum box and cut your own perspex lid for it

author: Kasper
author_rank: Frequent Contributor
timestamp: February 06, 2019, 06:55:46 am
content: Be careful what material you put infront of the IR sensor. Transparent to visible light does not mean transparent to IR. You also want immunity to sunlight if it's outside.I'm guessing by IR sensor, you mean PIR motion sensor? If thats true, safest bet is get a PIR with window (fresnel lens) with zones and detection distance that meets your specs. And don't put any other material infront of it.

author: jmaja
author_rank: Frequent Contributor
timestamp: February 06, 2019, 07:52:19 am
content: The IR is a a set of proximity sensors using a set of IR LED's. They work at 850 nm so very close to visible light. Seems to work OK through some clear plastics I have tested, but naturally the actual material to be used has to be tested as well.The goal is to measure visible light lx as well and the proximity sensor has a sunlight canceling system, which seems to allow measuring in direct sunlight.Then there are visible LED's to inform the user + BLE to send data to a mobile phone.Sensors and LED's are on both sides of the PCB thus the enclosure needs to be transparent or have windows on both sides.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 06, 2019, 07:59:35 am
content: For prototype qtys :a) two lids from Hammond clear plastic boxes, back-to-back.b) a sandwich of 2 sheets of acrylic, with a spacer frame +PCB in the middleFor production, the tooling cost for an injection mould for a simple shape like this wouldn't be very expensive

author: jmaja
author_rank: Frequent Contributor
timestamp: February 10, 2019, 09:52:32 am
content: I ordered some clear heat shrink tubing and did some testing.https://www.digikey.fi/product-detail/en/3m/FP301-1-48--CLEAR-24-PCS/3M161366-ND/3864906This one has no adhesive.The IR proximity sensor seems to work just fine through it. It increases the base level, but SNR is about the same.The PCB+battery is now about 24x61x4 mm. If I use the heat shrink tube, how could I seal the ends?I'm starting to like the idea of "plastic wrapping". What other ways are there to achieve this? Vacuum bagging? Laminating?

author: Kasper
author_rank: Frequent Contributor
timestamp: February 10, 2019, 05:08:16 pm
content: I like using hot glue to seal the ends of heat shrink tubing but thats usually with much smaller tubing and I've never tested its waterproofing quality.You could try hot glue then pinch with needle nose pliers to crimp it shut.

author: Nusa
author_rank: Super Contributor
timestamp: February 10, 2019, 07:51:06 pm
content: I've used hot glue with personal one-off projects. Should be fine for a prototype...you'll have to evaluate it for production. Can be smoothed when hot and trimmed with a knife when cold.For cold glues, I suspect super glue would work. Never tried myself.My other idea would be using the right size end plug for the tube to shrink around. In your case, perhaps a 4-5 mm thick sheet of plastic or wood cut to the width of the pcb. Butt pieces up to the pcb ends, shrink the tube, then cut both ends off to get nice edges. If you make the plugged ends long enough, you can drill them for mounting holes.

author: reboots
author_rank: Regular Contributor
timestamp: February 10, 2019, 08:46:29 pm
content: This is a little more than 6mm thick, but it might fit your other requirements:http://www.witzsportcases.com/id-badge-holders/see-it-safe-new.htmlWaterproof PVC badge holders are a common product. This listing ships from USA, but something similar may be available within your locale:https://www.ebay.com/itm/183568594557You will definitely want to test the waterproof claim. As other commenters have mentioned, clear plastics (especially PVC) won't last forever outside.

author: jmaja
author_rank: Frequent Contributor
timestamp: April 12, 2019, 06:51:05 am
content: Clear polyolefin heatsink from 3M worked OK and it was possible to seal the ends by melting. I could not find one with glue.However, I'm trying to go forward with a custom enclosure made from polycarbonate. I have designed it to be openable and sealed with an O-ring. The O-ring is set up as piston cylinder style.The PCB became even thinner (3.1 mm) allowing the enclosure to be only 4.7 mm. Now my problem is to find suitable screws for such a small and thin enclosure. The screws need to be recessed into the enclosure. The total lenght of the screw (including the head) must be less than 4.5 mm, preferably 4 mm to allow some tolerance. The thickness of the enclosure halfs at the screws is 2.2 mm, since there will be 0.3 mm thick fabric in between. Due to O-ring configuration no compression from screws is needed, it's enough to just keep the halfs together.The first installation and possible battery change after a few years is done by the user. The screws must work at least 3 times.What kind of screws would fit this application? Thread forming screws or machine screws? What kind of nut arrangement for the latter?The suitable size would be M2 (or #2). Thread forming at only 4 mm length are very hard to find and surpricingly expencive. Will they hold with such a short thread? Only 1.5-2 mm.Also M2 thread incerts for only 2.2 mm thickness are hard to find. I found one, but it seems not designed for recessed installation. Square or hexagonal nuts can be found at 1.2 mm thickness. Would making a recession for it work?The screws need to tolarate weather. Maybe A2 or brass is OK?At least the first enclosures will be CNC machined, since the mold cost approximations I have got have been 5 000-10 000 €. Is that expected?

author: jmaja
author_rank: Frequent Contributor
timestamp: April 12, 2019, 08:01:19 am
content: Would even tapping M2 threads to this 2.2 mm thick half work? Obviously not anymore, if the enclosure will be molded.

author: Skashkash
author_rank: Regular Contributor
timestamp: April 12, 2019, 09:05:01 am
content: Since we are throwing ideas out there.Impulse seal it in pouch?Like these marker lights (as an example)https://countycomm.com/collections/all/products/maratac-mas-micro-adhesive-strobe-3-pack-u-s-a-nsn?variant=20534147317830May want a top stiffener piece of pcb or plastic on top of circuitry. Extend ends and punch mounting holes like a luggage tag.

author: jmaja
author_rank: Frequent Contributor
timestamp: April 12, 2019, 09:56:25 am
content: That might be a good option for the heatshrink, but I also need to have a stiff option that allows changing the battery and different kind of installation.I took a quick survey of what I found on my desk. Two scientific calculators from the 80's. Phillips had M2x5 machine screws that seemed to screw into thread inserts. Casio had 2x6.5 mm thread forming screws into plastic. My old Samsung S4 Mini had M1.4x4 machine screws that probably screw into metal frame (didn't open it just took one screw out). MR16 LED "bulb" had M2x4 machine holding the PCB and screwing into metal (aluminium?) frame.All of these seem to open and tighten just fine.

author: reboots
author_rank: Regular Contributor
timestamp: April 13, 2019, 07:36:26 pm
content: Be aware that custom-machined polycarbonate, particularly using screw closures, may lead to serious problems with stress concentration and cracking. Do not allow your machine shop to use any kind of process coolant or lubricant other than water.I recommend producing a set of prototype enclosures of the final intended design, using material from your expected production supplier, and torture-testing them for as long as possible to make sure that e.g. thermal cycling won't cause stress cracking at the screw threads.I have had some luck with Plastite trilobular thread-forming screws in molded polycarbonate enclosures.The calculator enclosures you mentioned are likely made from ABS or similar plastic, which is softer and less prone to stress concentration.

author: jmaja
author_rank: Frequent Contributor
timestamp: April 15, 2019, 05:15:45 am
content: Quote from: reboots on April 13, 2019, 07:36:26 pmAre threads cut to PC the most likely problem? Would using a recession for a nut or a thread insert make these problems less likely? This thread insert would be thin enough (even when recessed):https://www.tappex.co.uk/products/brass-threaded-inserts/microbarbThe first enclosure prototype will be made tomorrow. If that seems feasible, the plan is to make ~20 and test them for 6 months before going further.

author: Nusa
author_rank: Super Contributor
timestamp: April 15, 2019, 05:54:52 am
content: If you design your case to have interlocking hinges arrangement on opposing sides (or even all four sides), you wouldn't need screws at all. Wire pins through the hinges would keep it closed. Easily removed for battery changes.

author: reboots
author_rank: Regular Contributor
timestamp: April 15, 2019, 01:27:20 pm
content: Quote from: jmaja on April 15, 2019, 05:15:45 amI have not used threaded inserts in polycarbonate, so I can't say. I would try oversized holes with minimal barb engagement, just enough to keep the inserts placed. I know some manufactures of polycarbonate enclosures use inserts, but those might be overmolded.

author: jmaja
author_rank: Frequent Contributor
timestamp: April 16, 2019, 06:56:23 am
content: Quote from: reboots on April 13, 2019, 07:36:26 pmWhat is the reasoning behind this? Machine shop would like to use the same cutting fluid mixture they use for other stuff. Mainly water, but does include other stuff to make it non-corrosive and better lubricant. Is PC sensitive to these chemicals?

author: Ian.M
author_rank: Super Contributor
timestamp: April 16, 2019, 10:38:37 am
content: Quote from: jmaja on April 16, 2019, 06:56:23 amVery! If exposed to the wrong solvents or certain oils, Polycarbonate becomes very brittle and then cracks readily and can even craze like broken safety glass just from internal stresses and diurnal temperature cycling.https://www.theplasticshop.co.uk/plastic_technical_data_sheets/chemical_resistance_guide_polycarbonate_sheet.pdfA little dish soap can be added to the water to lubricate the cut as well as cool it, but you wont be popular with the machine shop unless they are set up for a lot of plastics work with a separate mill, free from metal cutting fluids, as the dish soap will FUBAR their soluble oil coolant and may wash away too much oil from the mill table mechanism causing it to rust.

author: Psi
author_rank: Super Contributor
timestamp: April 16, 2019, 10:53:19 am
content: +1 for heatshink tubing.Not the normal heatshrink though, you can get special stuff that is thinner than normal heatshrink and sets much harder.It's the stuff used on RC speed controllers and the like.I think it's usually called 'thin wall' or 'ultra thin wall'

author: jmaja
author_rank: Frequent Contributor
timestamp: April 16, 2019, 02:47:30 pm
content: Machining seems to be quite challenging. The 6 mm thick part we used as stock bends too easily making very difficult to get the thin walls (0.8 mm) right. One had 0.8 mm, but the next only 0.45 mm, which was way too flexible, but still surprisingly difficult to break. I even hit it with a hammer (not that hard) and it survived. The enclosure appears to be too flexible in total making it probably leak in use. It's now only 4.7 mm thick with 0.6-2.2 mm walls. Probably will try to use ~6 mm total thickness allowing for 1.2-2.8 mm walls and more margin for the O-ring.

author: reboots
author_rank: Regular Contributor
timestamp: April 16, 2019, 04:20:31 pm
content: Quote from: Ian.M on April 16, 2019, 10:38:37 amSeconding Ian.M's explanation, which describes my experience. As as alternative, your machine shop might prefer to machine dry with compressed air for cooling and chip removal. You may still need to wash the parts in detergent to remove any oils from the tooling.