Author Topic: Simblee MSL  (Read 610 times)

Tim

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Simblee MSL
« on: May 26, 2017, 06:50:09 PM »
Hi all,

Have been learning all about MSL (Moisture Sensitivity Level). Recently, distributors have been affixing MSL caution labels to the ESD bags Simblees are shipped in, stating level 3. I wrote support@rfdigital.com and received word that Simblee is actually rated MSL 6. This means chips need to be baked (8-12 hours at 125°C) before mounting/reflowing, and following baking, the chips need to be mounted/reflowed within 6 hours.

We've never baked before mounting/reflowing. We've been hand assembling (using stencil to apply solder paste, hand placing components, including Simblee, then reflowing in reflow oven) and have been getting a failure rate of around 1 in 10. I'm waiting for reply from RF Digital with their opinion about the possibility that not baking Simblee before mounting/reflowing is contributing to the failure rate. Although we are not happy to learn about the baking requirement (which increases assembly time and cost), we'll be happy if baking prior to mounting/reflowing reduces our failure rate.

Any experience out there?

Many thanks,

Tim

Wayne

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Re: Simblee MSL
« Reply #1 on: May 27, 2017, 04:43:35 AM »
I have 3 proto boards being made and populated by a local house here. 
Will find out in a bit..

Tim

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Re: Simblee MSL
« Reply #2 on: June 05, 2017, 08:37:29 PM »
A bit of new information. We recently assembled 10 boards containing Simblee with 0% fail rate. Two things were different:

1) We used PCBs with pads for unused Simblee pins removed (less chance of solder bridging).

2) We pre-baked Simblees for 8 hours at 125°C.

We speculate that pre-baking is the change that brought improvement. Next we will assemble some boards with all Simblee pads and, again, pre-bake prior to reflow. If success, then more evidence that pre-baking is essential.

RFD_Patty

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Re: Simblee MSL
« Reply #3 on: June 08, 2017, 11:42:45 AM »
Tim -

We recommend bake before use per MSL 6.     

Happy to see you are getting better results.


Tim

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Re: Simblee MSL
« Reply #4 on: June 08, 2017, 05:14:09 PM »
Thanks Patty. I've read in some of your other posts that life at Simblee/RF/Heptagon/... has been rather busy, so I understand it taking time to get to certain things. I'll quickly point out that:

- Your current data sheet says MSL rating is TBD.

- Your distributors are classifying Simblee as MSL 3.

If moisture is in fact the cause of our assembly failures, we could have saved a lot of money (20-30 Simblees damaged as a result) had we known Simblee is MSL 6 at the start.

Glad we've likely found the culprit in our process. Thank you for your confirmation.

Tim

Wayne

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Re: Simblee MSL
« Reply #5 on: June 09, 2017, 05:52:23 AM »
Well, we will have a few boards done, and I have sent 1 board house this info.  I have a funny feeling they will not bake the chip on the 1st round.
He said he has never done this before.  But I'm sending him the datasheet so he can see the mounting of the Simblee.

I should have these boards in a week or so.

Tim, what board house do you use, for once this gets going, we will need lots of boards populated.
Since your board house will now be familiar with the product.
 

Wayne

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Re: Simblee MSL
« Reply #6 on: June 09, 2017, 08:10:15 AM »
Tim, can you tell me the area you live in.  I'm here in Utah and it is extremely dry.. Not like Arizona, but close.  We might not need to bake as long or at all

Tim

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Re: Simblee MSL
« Reply #7 on: June 09, 2017, 09:07:46 AM »
Hi Wayne,

We're in Alberta, Canada. Definitely dry in the winter. Interestingly, as spring approached, our failure rate increased significantly - more evidence that moisture has been our issue.

We hand assemble our boards. We use oshpark.com as our board fab, oshstencil.com for stainless steel stencils. We apply solder paste, hand place SMD parts (including Simblee) then reflow in whizoo.com reflow oven. We use a USB microscope to be sure Simblee is accurately placed on pads. We've added copper registration marks for Simblee on our PCB to aid in positioning because silkscreen is not always precisely positioned relative to the copper pads.

RF Digital support is stressing bake before use as per MSL 6.

Hope helpful ...

Tim

Tim

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Re: Simblee MSL
« Reply #8 on: June 17, 2017, 10:06:18 PM »
A quick update ... We've now hand assembled 21 boards with 0% failure. These boards do not have pads for unused Simblee pins. We also assembled 3 boards that have pads for all Simblee pins with 0% failure. It's starting to look clear that moisture (i.e. not pre-baking before reflowing) has been the cause of our high failure rate. What a relief to have solved the mystery.

It's not clear to me if there's an advantage either way to keeping or removing pads on board for unused Simblee pins.

Thanks all for your contributions to this thread.

Tim