Testing BGA uC before use - Page 1
Forum section: electronics / general

author: Jean_valjean
author_rank: Newbie
timestamp: April 06, 2022, 10:53:36 am
content: Ladies and Gentlemen,I am pretty sure someone has already had a similar problem like me:We have to buy a BGA uC from an unreliable source. Since we don't want to risk the whole PCB due to a - possibly - fake micro, we'd like to test it before assembling.Our idea is: we sacrifice one board. Solder a socket on it, then we can test every uC in this socket, one by one. In case it works well, we're sending these to the assembly line.Quantity is 1 - 200 pcs per year.My question is: has anyone of You already done such a task? What are the bottlenecks of it? Where can we buy 1-2 pcs of appropriate sockets?The microcontroller is encapsulated in a SOT1535-1 package, which is a 144 pin BGA, 1mm raster. On the board, there are virually no space around the uC, maximum 1mm around. The height is not a problem and the bandwidth of signals are not high, just a few MHz on the clock line.Thank You in advance for any help or advice.

author: mon2
author_rank: Frequent Contributor
timestamp: April 06, 2022, 06:30:02 pm
content: Contact this company with your requirements and post your updates in this thread. You will need to layout a pcb to support the pinout of the test socket but they should have a solution.http://andktech.com/

author: ataradov
author_rank: Super Contributor
timestamp: April 06, 2022, 06:53:22 pm
content: I don't think small footprint BGA sockets exist. They all require a lot of board area for mounting hardware.

author: free_electron
author_rank: Super Contributor
timestamp: April 06, 2022, 07:14:03 pm
content: Quote from: ataradov on April 06, 2022, 06:53:22 pmyes they do. they use a special material from 3M called Z-connect.Ironwood makes those.Z-connect is polymer that has tiny strands of tungsten in it under a slight angle.ACF is similar but uses silver particles :https://multimedia.3m.com/mws/media/296669O/3mtm-anisotropic-conductive-film-adhesive-get-connected.pdfall you need is about 4mm around the bga to hold the frame. but you need 4 screw holes to pull it in...

author: ataradov
author_rank: Super Contributor
timestamp: April 06, 2022, 08:16:14 pm
content: Quote from: free_electron on April 06, 2022, 07:14:03 pmYes, I'm aware of this. But as you said, you can't mount that given " there are virually no space around the uC, maximum 1mm around." You have to redesign the board for that.In theory it should be possible to make a connector like this using springy contacts on the DUT side and solder pads on the PCB side. This way it would mount right on the PCB and will only require additional space above the board. But I assume this is deemed to be too fragile for practical use.

author: Jean_valjean
author_rank: Newbie
timestamp: April 07, 2022, 05:48:23 am
content: Gentlemen,thank You for all the ideas.Yesteray I asked Ironwood for help, hopefully they will answer soon.I also study the product range of andktech. Thank You mon2, I didn't know this company.When I have to redesign the PCB, I would do it with another uC, which is available on the market. (available -) It's a better solution than testing unreliable supplier's products. But redesign is the thing I'd like to avoid, because it results a lot of extra work - porting the firmware, testing the whole product, a new EMC control which isn't cheap.Thanks again for the ideas!

author: james_s
author_rank: Super Contributor
timestamp: April 07, 2022, 06:03:41 am
content: What about designing a minimal test board just to test the microcontrollers? Something that has power, a clock, programming header and maybe a few LEDs? I think if the chip detects correctly and you can program it to blink an LED then it's probably legit.

author: MathWizard
author_rank: Super Contributor
timestamp: April 07, 2022, 05:16:57 pm
content: bed of nails? /pins?

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 07, 2022, 05:51:39 pm
content: Quote from: james_s on April 07, 2022, 06:03:41 amThat's what I was gonna suggest. Why bother reusing the existing PCB when it was clearly not designed as a test tool, and trying to find a small enough BGA test socket that would fit (in times of global shortage of pretty much everything), while designing a custom board for this would put no constraint on the test socket or anything else.

author: Jean_valjean
author_rank: Newbie
timestamp: April 08, 2022, 06:13:57 am
content: Gentlemen,It seems, Ironwood has a solution for this challenge. They offer an adapter, which is not larger than the IC itself, but raises the test socket higher from the PCB. It can work, there are more space 2.5mm above the board and no holes are necessary. However, this whole thing must only be on my own desk, it is mechanically not robust enough to give it away.Why I don't make a test-board? Because there are a wealth of peripherals in this uC. It's one out of the Kinetis K60 series. We use a lot of internal peripherals, and in case we can only buy a fake component, it may happen that almost everything is OK, but one of these peripherals aren't. The simplest test is to have an original board, load the original FW into the processor and test the whole thing together.A few years before I already burned my hand with fake components. I'm not willing to do it again.Thanks for all the comments!

author: ataradov
author_rank: Super Contributor
timestamp: April 08, 2022, 06:26:49 am
content: Do they have part numbers or drawings for that adapter? It sounds like something I described, but I have never seen that done in practice.The mechanical part is probably solvable with some epoxy. But another thing to keep in mind is that all those sockets have very limited number of insertions, often lower than 100.

author: Jean_valjean
author_rank: Newbie
timestamp: April 08, 2022, 01:14:36 pm
content: > Do they have part numbers or drawings for that adapter?Of course, they do.Adapter, to be soldered onto the board: SF-BGA144C-B-42Through hole adapter, to be plugged into the previous adapter: LS-BGA144C-05And the BGA socket on top of all these: SG-BGA-6204You can find them athttps://www.ironwoodelectronics.com> those sockets have very limited number of insertions, often lower than 100.It's just all right, it helps us. We don't need thousands of controllers.

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2022, 05:49:57 pm
content: Quote from: Jean_valjean on April 08, 2022, 06:13:57 amI think it's highly unlikely you will find a fake part that identifies and programs like a genuine part but has some peripherals that don't work. Does anyone know of an example like this happening?

author: thm_w
author_rank: Super Contributor
timestamp: April 08, 2022, 09:38:04 pm
content: Quote from: james_s on April 08, 2022, 05:49:57 pmTechnically some of the STM32 clones fit this, the peripherals work, but not in exactly the same way as the original. So end result could be that that USB does not enumerate.I'm not aware of Kinetis K60 clones though.

author: harerod
author_rank: Frequent Contributor
timestamp: April 10, 2022, 07:16:37 pm
content: Jean_valjean, the current situation forces many of us to buy from sources that we would rather avoid.The BGA sockets look interesting. I didn't see pricing on the website, though. From hearsay I remember horror stories regarding price and reliability.Having said that, even if you are not equipped to do this, your board assembly partner should be able to replace BGA's on populated boards. Provided you have the correct tools, testing a rather small sample size on an actual production board might be the simplest and overall most cost effective solution.When I got a batch of brokered STM32's, I did exactly that. For TQFP I am equipped here, for BGA I might ask the assembly factory.

author: mac.6
author_rank: Regular Contributor
timestamp: April 11, 2022, 06:42:41 am
content: We use ironwood on mostly all our socketed evaluation board without any issue to date.I won't use them for extensive testing as they are not meant to (just do a sample of your batch is enough to quantify the quality of it).A simple allen screw press the chip, so be sure to get a good low torque screwdriver to avoid stressing the pads.

author: harerod
author_rank: Frequent Contributor
timestamp: April 11, 2022, 10:12:52 am
content: mac.6 - thanks for the info. Could you share some indicator, regarding price of the connectors? Where do you buy those?

author: Jean_valjean
author_rank: Newbie
timestamp: April 12, 2022, 07:18:55 am
content: The distributor of Ironwood in Germany is:www.emc.deThey are very helpful. I got a quote from them already.You will get it too, I am sure. Just sit down before read it :-) to avoid any unpleasant accident :-)

author: harerod
author_rank: Frequent Contributor
timestamp: April 12, 2022, 11:18:24 am
content: Well, you could stop beating around the bushes and give some ballpark pricing.For various reasons (cost, reliability, cycles, ...) I have used the last ZIF-socket for a larger pincount MCU at the turn of the millenium.If we are talking about small sample sizes, a skilled technician with adequate equipment will be rather competitive in directly replacing the component.

author: mac.6
author_rank: Regular Contributor
timestamp: April 12, 2022, 03:44:54 pm
content: Quote from: harerod on April 11, 2022, 10:12:52 amNot a single clue, dev board are outsourced. But final price is a four figure per board at least, so not an issue when you are dealing with a multi-millions projects.