good point. never consider that could be a factor...
On Dec 4, 2017, at 10:52 AM, Stadem, Richard D wrote:

> In the past I had to qualify MEMS for a production line, to ensure  
> no shock or vibration was seen that could possibly hurt the  
> components. These were found to be very susceptible to failure.
> I used an amplified accelerometer to measure the shock and  
> vibration from the manufacturer, on the truck or plane, and through  
> the processes.
> We discovered that irregular shock and short vibration exposure did  
> little to harm the MEMS.
> What did kill the micromechanical parts was resonant vibration, and  
> we also discovered that certain MEMS were susceptible to their own  
> particular steady-state vibration frequencies and multiples of  
> those frequencies.
> Where did these show up?
> ONLY IN THE WATER WASH PROCESS!
> Weird, eh?
> Had nothing to do with moisture ingression to the package itself.  
> The transmitter worked even underwater, and the machine's large  
> pump motors caused a huge cavitation effect when transmitted  
> through the water. The spray sometimes killed the MEMS also, but  
> mostly it is cavitation while fully immersed.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce  
> Koo
> Sent: Monday, December 04, 2017 9:19 AM
> To: [log in to unmask]
> Subject: Re: [TN] board wash / non-washable modules - the dilemma
>
> if your module is RF MEMS, (since it is susceptible to moisture, it  
> might have opening or movable parts that can change stiffness or  
> sticking when expose to moisture), wash is not good... you never  
> can bake out fully in those micro-opening... sticking due to  
> combination of flux residue (not much, just tiny bit) and moisture  
> will kill you (it might work fine on marginal spec, but when it  
> aging, you see difference out of spec quickly, like within  
> warrantee period of 6 month-ish when use it high humidity  
> condition..).  IMHO.  Best of luck.
> jk
> On Dec 4, 2017, at 8:48 AM, Graham Collins wrote:
>
>> Thanks for all the (varied) opinions!  No consensus here.
>>
>> We are a build to print shop, so I'm not responsible to dictate  
>> how to
>> put it on - my obligation is to point out the issue and recommend a
>> solution.  I'm going to recommend the "attach last by hand using
>> no-clean flux" method, it will work on this application
>> as the module has castellation terminations, accessible by hand.
>> If it was bottom terminations only I'd be facing a bigger problem, in
>> that case I would recommend the "wash and bake".
>>
>> cheers,
>>
>>  Graham
>>
>> regards,
>>
>> Graham Collins
>> Senior Process Engineer
>> Sunsel Systems
>> (902) 444-7867
>>
>> On 12/1/2017 4:37 PM, Richard Kraszewski wrote:
>>
>> Ditto  to Bob's thought. Localized clean if need be.
>>
>> Rich  Kraszewski
>> Senior Staff Process Engineer
>> Plexus Engineering Solutions
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann
>> Sent: Friday, December 01, 2017 12:28 PM
>> To: [log in to unmask]<mailto:[log in to unmask]>
>> Subject: Re: [TN] board wash / non-washable modules - the dilemma
>>
>> My vote because this is what we have done for small Proto builds  
>> is to
>> leave the module off, build and wash w water soluble flux then  
>> install
>> the RF module using the no-clean?
>>
>> Bob Wettermann
>> BEST Inc
>> Your BEST source for PCB Rework/Repair, Training and Tools
>> 847-767-5745
>>
>>
>>
>>
>> On Dec 1, 2017, at 10:15 AM, Tom Brendlinger
>> <[log in to unmask]><mailto:[log in to unmask]> wrote:
>>
>> I have heard many times that in high humidity environments with very
>> small amounts of condensing humidity, no clean flux can become
>> re-activated. This paper discusses some options:
>> https://link.springer.com/article/10.1007/s11664-014-3609-0
>>
>> In my opinion, reach out to the part manufacturer and see if you can
>> perform cleaning in a particular way to not risk having issues.
>>
>> Tom
>>
>> On Fri, Dec 1, 2017 at 1:05 PM, Robert Kondner
>> <[log in to unmask]><mailto:[log in to unmask]>
>> wrote:
>>
>>
>>
>> I would go for wash and bake but I worry that washing will "Wash Crud
>> Into"
>> the shielded areas and the rinse will not rinse it out.
>>
>> Are your concerns about no clean flux in a marine environment really
>> justified or is it hog wash from somewhere?
>>
>> Bob K.
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
>> Sent: Friday, December 01, 2017 10:09 AM
>> To: [log in to unmask]<mailto:[log in to unmask]>
>> Subject: [TN] board wash / non-washable modules - the dilemma
>>
>> Hello Technet!
>>
>> Wondering what other people are doing with this dilemma.
>>
>> We have had several customers design in pre-built RF modules on their
>> boards.  I totally get why, it is a pre-built, FCC approved, easy
>> solution
>> -
>> the fastest way to get a good Wi-Fi or bluetooth solution.
>>
>> Where things go off the rails for me are where this is used in a high
>> humidity application (e.g. a marine setting).  We strongly prefer to
>> wash boards, we can build no-clean if needed but I'd prefer not to  
>> for
>> an on the water use.  But the part a customer has designed in
>> specifically says not to wash it (it has an EMI shield, so they are
>> properly concerned with water entrapment).
>>
>> So - would you:
>>
>> - build it no-clean?
>> - leave the part off, build and wash as usual, install RF module  
>> later
>> using no-clean?
>> - wash it (and maybe bake it to dry it out)?
>> - ????
>>
>> --
>> regards,
>>
>> Graham Collins
>> Senior Process Engineer
>> Sunsel Systems
>> (902) 444-7867