Custom Trays for PNP assembly - Best Material? - Page 1
Forum section: electronics / general

author: mrpackethead
author_rank: Super Contributor
timestamp: August 18, 2017, 01:33:33 am
content: From time to time, i'd like to be able to make a custom flat tray for putting 'odd' parts in, or somethign i dont' have a JEDEC tray for..I was wondering what the best material would be to use. I'd though about using aliumnum and milling it.. ( that woudl be a reletively simple task, since i have the tools to do this ).. however, i was put off this, when it was poitned out to me that ESD wise thats a bad idea, when the alumium surface oxidises and is no longer conductive..Any suggestions?

author: KL27x
author_rank: Super Contributor
timestamp: August 20, 2017, 08:26:20 am
content: I was waiting for others to weigh in. ESD is something of a religion, and I hate to wade into that territory.Peronally, with my limited experience in machining stuff, I would for sure use aluminum. If ESD turns out to not be a problem, then you're set. If it does, then you will have to do some more hard work to figure out what to use.In terms of rigidity, weight, durability, and DEBURRING (or lack thereof of aluminum vs plastic), you will have a hard time to beat aluminum.I am not going to weigh in heavily on ESD this or that, but I store CMOS stuff in brass tubes for several years, now, without any problem. The brass tarnishes, but it's not as tough a coating as aluminum oxide. Still I bet it's enough to prevent an electrical contact for the tiny SMD components resting in the tubes. I don't believe aluminum is known to be particularly triboelectric with other common materials in way that you could, say, build significant charge on glass by rubbing it with wool (which I say as just an example from memory which may be completely incorrect, but you get the idea).

author: sleemanj
author_rank: Super Contributor
timestamp: August 20, 2017, 09:49:12 am
content: Have you a 3d printer? You can get mildly conductive filament which should be suitable (indeed it's usually advertised as for "anti static" use), unfortunately I've only seen it in ABS on Aliexpress, since I don't print ABS I've never bought any to try.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 20, 2017, 10:24:45 am
content: For ESD the last thing you want is a highly conductive surface. People often concentrate on the "ES", where it's the "D" that can cause damage.However for individual parts, they are small enough that ESD isn't going to be an issue as they have so little capacitance that you'd struggle to get any significant discharge.For a SMD parts tray, no material is going to be an issue ESD-wise - the primary consideration is mechanical - how easy to machine, lack of electrostatic stickyness, non dust-producing etc.IMO the only time ESD can be a practical risk is on an assembled board, as the board as a whole is big enough to to build up a charge that gets discharged when touched, or has sufficient capacitance to ground that a touch from a charged person can cause enough current flow to cause damage.

author: IconicPCB
author_rank: Super Contributor
timestamp: August 20, 2017, 11:03:17 am
content: Aluminium is not necessarily a bad choice provided you can get it alodined.

author: jmelson
author_rank: Super Contributor
timestamp: August 20, 2017, 07:13:46 pm
content: Quote from: mrpackethead on August 18, 2017, 01:33:33 amIf you hard anodized the aluminum, then MAYBE it would be a bad idea. I still think even that would be able to conduct away and serious charge quickly. But, bare machined aluminum will not have enough of an insulating layer to retain any charge for long (like milliseconds). Now, highly conductive materials are not so great with the charged device model, but you should not allow your parts to get charged up in a proper workspace.

author: mrpackethead
author_rank: Super Contributor
timestamp: August 21, 2017, 07:44:53 pm
content: Aluminuim it is. :-)I'm going to machine this up today all thigns being equal. This one is for some 9x9mm TQFN's... These will only take a few minutes of machine time to make, but will be somethign ill have for a long time.

author: jmelson
author_rank: Super Contributor
timestamp: August 21, 2017, 08:09:29 pm
content: Quote from: mrpackethead on August 21, 2017, 07:44:53 pmOf course, I keep at least two of every size tray I have ever had. That way, I can load chips into the tray (if the accursed distributor puts them in tapes cut into lengths of 5, which can't be fed through a feeder in my P&P machine. Yes, I mean YOU, Digi-Key!)With two trays, I can load chips into one, then put another over top and take it to the P&P, and after placing on the tray holder, I take the top tray off. That prevents accidents with chips all over the floor while I'm carrying them. You don't have to jostle an uncovered tray very much for the chips to go flying.Jon

author: mrpackethead
author_rank: Super Contributor
timestamp: August 21, 2017, 09:05:53 pm
content: I had this exact problem last week. Old product that client wanted, and i needed 40 chips.. got 8 strips of 5 from Digikey..

author: KL27x
author_rank: Super Contributor
timestamp: August 22, 2017, 07:21:19 am
content: I have largely avoided QFP where possible, and this has me curious.QuoteSo what does Mouser do?QuoteAlso curious.... how many different kinds are there? Do all the different manufacturers use one standard OEM/tray size for a given package?I have used QFP just once, and dealing with 160 chip trays without a PnP machine was pretty aggravating. QFN preferred, where possible.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 22, 2017, 07:42:06 am
content: Quote from: KL27x on August 22, 2017, 07:21:19 amDigikey can be inconsistent in how they supply parts marked as "Cut Tape", but I think you can specify single lengths of tape in the order instructions, if you remember...

author: TheSteve
author_rank: Unknown
timestamp: August 22, 2017, 08:08:13 am
content: We have machined custom trays using ABS plastic. It has always worked quite nicely. We have not used them to mount any components that are overly sensitive to static. We have also just made a row of chips and had our machine pick them up with no tray at all. It worked great for 50 FT232RL chips we had that were not in tape.

author: mrpackethead
author_rank: Super Contributor
timestamp: August 22, 2017, 09:21:09 am
content: Made.