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Messages - Tim

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1
Support / Re: Simblee MSL
« 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

2
Support / Re: Simblee MSL
« 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

3
Support / Re: Simblee MSL
« 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

4
Support / Re: Simblee MSL
« 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.

5
Support / 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

6
Support / Re: hand soldering Simblee module?
« on: May 25, 2017, 08:16:00 AM »
Hi Anthony,

You might find this thread helpful:

http://forum.rfduino.com/index.php?topic=1735.0

Cheers,

Tim

7
Support / Re: Simblee assembly and pick'n place machines
« on: May 25, 2017, 08:08:03 AM »
Some new information to share ...

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. I'm waiting for reply from RF Digital with their opinion about this possibly contributing to the failure rate we are experiencing. 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

8
Support / Re: Simblee assembly and pick'n place machines
« on: May 14, 2017, 01:49:45 PM »
Thanks Tom.

Another change in our process is to attach the programming header to the board before applying power to the USB shield. I understand damage can occur if I/O pins are connected before power is applied. The theory is beyond me, but I've learned this from a trusted source.

Tim

9
Support / Re: Simblee assembly and pick'n place machines
« on: May 14, 2017, 08:54:20 AM »
Some additional ideas in attempt to improve our hand assembly yield.

1) Change I/O pin assignment to reduce number of adjacent pins in use.

2) Remove from PCB any pads for Simblee pins not in use.

Reasonable?

Also, we've cleaned up our handling procedures to eliminate ESD events that could damage chips.

Thanks,

Tim

10
Support / Re: bad Simblee batch?
« on: April 24, 2017, 02:21:25 PM »
We'll be receiving more Simblees from DigiKey tomorrow and will be assembling. Results will be revealing. I also noticed different colour, but that could be because of rework. These are chips that were removed from boards after failure.

We recently ordered from Mouser because they were $3 cheaper. It could be coincidental that we started having assembly issues with this batch. Will post more here as we learn.

Thanks!

11
Support / bad Simblee batch?
« on: April 23, 2017, 01:14:33 PM »
Hi ..

Trying to explain why we're getting a high failure rate on assembling our boards. We recently ordered from Mouser and received 30 Simblees packaged as in photo, which means someone handled them to take from factory packaging and place on foam. Also found a label on the anti-static bag containing the Mouser order that have never seen before (see attached photo). Wondering about possible ESD events during handling and shipping that damaged chips. Previously all Simblees came from DigiKey and in original factory packaging and we had a much higher success rate. Wondering if anyone has had issues with Simblees arriving defected from different suppliers.

Appreciate any thoughts, experience.

Tim

12
Support / Re: Simblee assembly and pick'n place machines
« on: April 02, 2017, 04:26:57 PM »
Thanks Tolson. I'm hopeful that smearing flux on Simblee pads before overlaying stencil and applying solder paste will do the trick. Will post here again once we have a sense for helpfulness.

Thanks.

13
Simblee Libraries / Re: Simblee library 1.1.1
« on: April 02, 2017, 04:24:33 PM »
Thanks Tolson. Has 1.1.1 proven to be a stable release for iOS platform?

14
Simblee Libraries / Simblee library 1.1.1
« on: April 02, 2017, 08:28:19 AM »
Hi ...

I see that Simblee library 1.1.1 is available, but don't see any announcements about it. Anyone aware of details of the update? Release notes?

Thx,

Tim

15
Support / Re: Simblee assembly and pick'n place machines
« on: April 01, 2017, 08:51:09 AM »
A couple new ideas that might be helpful?

First, would applying extra flux to the Simblee pads on the PCB before applying solder paste with stencil be helpful?

Second, after applying solder paste to board (with stencil) and before placing Simblee, how about melting the solder paste over the Simblee pads with a soldering iron to get the solder attached to the tiny pads. At that point could make sure there are no solder bridges. Then position the Simblee over the pads and reflow.

Thoughts? Thanks,

Tim

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