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April 2008

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Tue, 15 Apr 2008 16:29:00 +0300
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text/plain
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text/plain (143 lines)
Not surprising he's concerned. I would be, too. 200 V/mm is a helluva 
gradient under normal conditions, let alone at 85/85. You will tear 
apart all the residual ions in FR-4 under those conditions. I would say 
the only possible way of ensuring electrical integrity is to make sure 
that everything is as clean as possible and then underfill/conformally 
coat with top quality resins.

Brian

Steve Kelly wrote:
> Good Morning,
> I need to ask some more questions on this thread. 
> One of the reasons our customer went to a water soluble paste was the high
> voltage/damp heat test requirement on the finished assembly.
> The test requirement is 1000 hours of damp heat test at 85C/85RH. The
> voltage requirement is 250 volts. BGA pad spacing is .050. The customer was
> concerned about passing this test. 
> Regards Steve Kelly
> 
> Steve Kelly
> PFC Flexible Circuits Limited
> PH: (416) 750-8433
> Fax: (416) 750-0016
> Cell: (416) 577-8433
> 
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly
> Sent: Monday, April 14, 2008 1:58 PM
> To: [log in to unmask]
> Subject: Re: [TN] Possible flux contamination issue
> 
> Thanks everyone for the help. Regards Steve Kelly
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> Sent: April-11-08 11:50 AM
> To: [log in to unmask]
> Subject: Re: [TN] Possible flux contamination issue
> 
> 24 years ago (yes 24!), I gave a paper at InterNepcon, in Brighton, UK, 
> entitled "Contamination on Components  and Small Assemblies". I no 
> longer have a copy, but I'm fairly sure I evoked the need to have all 
> the components supplied clean to avoid just this kind of problem.
> 
> Brian
> 
> Steve Kelly wrote:
>> Good Morning,
>>
>> We are assembling a BGA connector onto a flex circuit. The BGA has leaded
>> balls and the BGA manufacturer uses a no-clean process to attach the balls
>> to the connector and does not clean afterwards. 
>>
>> When we assemble the BGA connector to the flex we use water soluble paste
>> and then we clean. After damp heat cycling we have seen some shorts. When
> we
>> take off the connector we see flux residues on the underside of the
>> connector but not on the flex.  So my question is - what are the concerns
>> about mixing no-clean and water soluble? Is the failure likely due to
>> inadequate cleaning or is there something else I should be concerned
> about.
>> I realize this is probably not the way it should be done but some days you
>> just do what the customer wants - good or bad. Thanks in advance. Steve
>> Kelly
>>
>>  
>>
>> Steve Kelly
>>
>> (416) 750-8433 (work)
>>
>> (416) 750-0016 (fax)
>>
>> (416) 577-8433 (cell)
>>
>>  
>>
>>
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