Iteadstudio's flex PCB quality

Door mux op vrijdag 17 januari 2014 21:43 - Reacties (6)
Categorie: -, Views: 46.956

This is part two of a - probably - longer running series on PCB quality in the 'hobby' space. I say hobby space mainly because of prices, not necessarily quality. If you haven't done so already, I highly recommend reading my previous blog post about seeedstudio's 4 layer PCB quality for some background on the subject.

Overview of the PCB

For my work work I needed a flexible PCB that could fit inside more or less arbitrary electronics to function as a sensor. I didn't have any control over its position or shape, so the PCB had to be as flexible as possible to accomodate any usage scenario. Flexible PCBs (also called Flat Flex PCBs) of course immediately sprang to mind, but until very recently this technology was incredibly expensive - last time I ordered one from Cyner the invoice was well above 2000 euros for a small prototype. For some time however, Iteadstudio.com offered an up to 100x100mm flexible PCB manufacturing. That's past tense, because it seems right now that I'm writing this blog, they are discontinuing the service. However, after informing about this service, I heard from the PCB service behind Itead studio that they will be re-launching the product after the spring festival. The service is back, you can find it here. Prices are pretty great; $65 for 5x5cm up to $80 for 10x10cm.

Anyway, here's a rundown of my board

Board materialMylar 0.15mm
18µm copper thickness
Surface finishENIG (Electroless Nickel Immersion Gold) ~2µm
Board size34x50mm
Solder mask colorYellow
Amount ordered/received in good order10/10
Price$75 + $33 shipping (DHL)
Total time20 days


My flex PCB straight from iteadstudio

I have to say - this is an absolutely stunning PCB technology. The boards are incredibly thin. The substrate is actually a bit thinner than 150µm and very transparent. But not just the looks are good, the design rules are incredible. With 2/2 mil copper width/spacing (yes, you read that right) and lasercut vias, you can use this technology not just for flexible stuff, but also to break out extremely dense BGA packages for just $6.50 per PCB. And because almost everything in the process is lasercut, alignment and tolerances are absolutely stellar. Have a look at this:

Iteadstudio flex PCB alignment

This is almost a microscopic view of the PCB, looking at an 1812 Kelvin sense resistor footprint with a via to the other side. That has to be the roundest via you have ever seen. It's not a large via by any stretch of the imagination: it has a 10 mil hole, but the very thin plating and lack of fill makes it seem very wide. Anyway, also visible on the photo is the exceptional solder mask and especially board outline alignment. That there is copper within 5 mils (0.127mm) of the board edge. Nobody on conventional 0.6mm+ thickness FR-4 will allow this because of machining tolerances, but here you can.

Anyway, it's not all glorious. This is great technology to be able to use at a low price, but for FPC quality, it is not quite the best. The gold plating is even thinner than on their 2/4-layer service, and the plating is incomplete with rough edges at places where copper dives underneath the solder mask. Another small heckle I have is the horrendous silk screen:

Iteadstudio flex PCB silkscreen (1)
Iteadstudio flex PCB silkscreen (2)

That is some crusty silk screen, and this is especially bad on a flexible PCB. On one side lines are missing or very thin, on the other the lines are too thick and there are some extra blobs (e.g. the blob on the side of the '0' in 'rev0'). Alignment is not very good - look at how far that silkscreen has shifted inside the SOT-23 footprint. Also, the resolution is pitiful.

It seems to me that they use the same screen printer here as they do for other technologies, but the problem with that is: on flex PCBs, you want to use smaller components. Whereas 0402 is the smallest you can do with 6/6 design rules on their standard process, on here you would definitely want to go 0201 or 01005 with 0.4mm pitch QFNs and BGAs, and it is absolutely impossible to make part outlines on the silkscreen with this coarse of a screen printer. And another important problem with the silkscreen is its sheer thickness: it seems to be almost thicker than the copper and soldermask! I hope this service will switch to either a much finer mesh screen printer or even better photographic silkscreening in the future, which yields results like this (from Eurocircuits):

Eurocircuits silkscreen quality

Isn't that much better? Even though it's slightly overfilled, those (equally thick) lines have much better definition than Iteadstudio's service. By the way, that 1.6mm PCB now looks enormous, doesn't it?

However, even though it should have been obvious already, the most important feature of flexible PCBs is their... well, flexibility. I was worried they would mess this up or refuse to produce my design, but they did it and it worked briliantly. I am of course referring to the strip of very thin board in between the business end of my board and the connector side. Here is the board with components installed, and the bendy bit functional:

Iteadstudio flex PCB in action

Those are actually 2 mil wide traces, 6 in total (3 on top, 3 on the bottom), on a strip of mylar base material that is just 1.5mm wide. And they produced it without a problem! Unfortunately I could not get a lens close enough to the traces to show you how extremely clean the edges of those traces were, but I am actually confident that I could draw 1 mil traces and they would be able to produce it. Marvellous.

Oh, and also...

Een wonder!

They put the code in the little box I made for the code! They listened to me! Iteadstudio, just for this you can expect a lot more orders from me in the near future. And Seeedstudio, shame! Itead can do it, why don't you!

Conclusion

This has been part two of this series that shows the quality of cheap chinese PCB services, and I have to say I have been looking forward to this. Five years ago I was etching my own PCBs with toner transfer and horrible methods like that, and now for less than the cost of one hour's pay I can order 2/2 mil flex PCBs from China.

The quality is great for the price, but if anything I'd like the plating quality to be a bit better, the silkscreen definitely needs some more work and ideally - but this is honestly just a consequence of being pampered with other services - I'd like the turnaround to be a bit quicker. We've had 1-week turnaround for everything from 0.6 to 3.2mm PCBs for a couple years now with DHL shipping, so I'd like for FPCs to eventually get there too.

I hope this blog will help my fellow electronic design engineers and for now, happy designing!

Volgende: BBG Zuinige Server Maart 2014 03-'14 BBG Zuinige Server Maart 2014
Volgende: Seeedstudio 4-layer PCB quality 01-'14 Seeedstudio 4-layer PCB quality

Reacties


Door Tweakers user johnkeates, vrijdag 17 januari 2014 21:58

They put the code in the little box I made for the code! They listened to me!
I'm just loving this. Companies that do things like this win me over instantly.

Door Tweakers user mux, vrijdag 17 januari 2014 22:51

Yeah, just for that they're getting more traffic from me. It's actually pretty important for some applications of mine that they don't put extra artwork in certain places, so these couple of orders were a test case to see who would actually listen to me.

Anytime I'm designing a face plate or something like that, I'll choose Iteadstudio. Fun fact by the way, Eurocircuits of all places ignored my production notes :P (they usually don't though, I think this was just a one-time mistake).

Door Tweakers user Damic, zaterdag 18 januari 2014 00:23

DAMN that's sharp :o and cheap.

Door Tweakers user pientertje, zondag 19 januari 2014 20:28

What is the weight of this flex pcb? I'm building a small UAV where every gram counts, does it make sense to replace all normal pcb by flex-pcb?

Door Tweakers user mux, maandag 20 januari 2014 08:28

I don't have a scale that can accurately weigh this, but certainly! It is basically standard practice in (very) small RC aeroplanes and UAVs to always use flex PCB instead of regular FR-4 for PCBs, as there is no use for the extra weight and rigidity of standard PCB materials.

Door Andrew, zaterdag 30 januari 2016 17:33

Thank you for this review, and as I'm into PCB assembly myself it was very helpful. Seems like good quality in comparison to price I must say. Keep up the good work!
Andrew | www.nexpcb.com

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