Hi Graham,
I will be extremely grateful if you can send me a copy too. Thank you.
Yee T.G.
Hadco Corp.
______________________________ Reply Separator _________________________________
Subject: Re: [TN] RF Circuitry and Rosin Core Solder
Author: "TechNet E-Mail Forum." <[log in to unmask]>, at corp
Date: 1/25/98 10:26 AM
Karen,
I most certainly do have more background data: 7 years of detailed research
carried out by the Swedish
Research Institute for Production Engineering IVF in Gothenburg, Sweden 1989
to 1996. Further, research carried out using SIR testing via the British
Collaborative CFC Elimination Project run by the British National Physical
Laboratory in conjunction with British Aerospace, GEC Hirst Research and Bell
Northern Research through the British Government, DTI 1989 to 1993.
Through this work, it was found that certain synergistic influences were at
work and that there were numerous anomalies between the prevailing SIR test
parameters and the research values produced.
I will make every endeavour to get you copies where this is on general
release. It was partly a result of this work that the new ISO working group
was formed to
further evolve the J-STD-004 and apply SIR teesting as a valuable method of
predicting circuit reliability
Graham Naisbitt
__________________________________________________________________________
[log in to unmask]
Concoat Ltd
Alasan House, Albany Park
Camberley GU15 2PL UK http://www.concoat.co.uk
Application Engineers in Chemical Compounds to the Electronics Industry
-----Original Message-----
From: Karen Tellefsen <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 23 January 1998 08:42
Subject: Re: [TN] RF Circuitry and Rosin Core Solder
>Whoa there! Do you have good references for this?
>Not SMT or Circuits Assembly, I mean something tougher
>peer review like Electrochimica Acta or J. Electrochem Soc.
>
>1. Electromigration requires DC voltages and currents.
>
> a. AC voltages and and current will not cause
> the electrodissolution of copper, silver,
> tin or lead. The only materials that corrode
> with imposed AC (<~10 kHz). are amphoteric
> materials, like aluminum.
>
> b. AC voltage and currents will not allow the
> the electrodeposition of any metal that I know.
> The metal deposited during one half wave will
> dissolved during the 2nd half wave.
>
>2. Imposing a small AC voltage (5 to 50 mV) on top
> of a DC voltage and looking at the resulting
> small AC current is good way of studying
> electrochemical reactions like dissolution and
> deposition of metals. The frequencies used range
> from 1 mHz to 100 kHz. Frequencies over 100 kHz,
> such as RF, are not useful for looking at
> electrochemical reactions because the chemical
> kinetics of these reactions are too slow.
>
>BTW 20 min. is ~ 1 mHz, and RF is >.5 GHz.
>
>The problem with rosin/resin residues is that they have
>interesting dielectic properties. Leaving this residue
>on a PCB board may change the RF properties that an RF
>engineer spent a long time considering wrt the board,
>especially if a lot of this residue is left on the board.
>These effects have been examined by the Sandia and
>the Georgia Tech studies to a small extent.
>
>
>Graham Naisbitt wrote:
>>
>> Mark,
>>
>> Given that all fluxes leave residues, the issue is how will they
inter-react
>> with the other process chemistries you have on your assembly.
>>
>> In addition, we know that the higher the operating frequency, the more
the
>> electrons migrate to the periphery of the conductor so, where they
interface
>> with the board surface, you will have an area of high potential for
>> electro-chemical reactions.
>>
>> Are you able to predict these and verify that they will not be harmful to
>> long term reliability? SIR testing developments will permit you to do
this
>> by measuring the amount of leakage that is occurring. Use a voltage
gradient
>> of 100v/mm that will better mimic your assembly operating conditions,
apply
>> frequent monitoring so that you do not miss any dendrite formations
>> (electro-chemical migration) and use current limiting resistors to
preserve
>> them for further analysis. Bear in mind that dendrites are known to form
>> within 20 minutes under the right conditions.
>>
>> You should then be better placed to determine the reliability of your
>> assembly. I hope this helps - let me know if you would like more
>>
>> Graham Naisbitt
>>
>>
__________________________________________________________________________
>>
>> [log in to unmask]
>>
>> Concoat Ltd
>> Alasan House, Albany Park
>> Camberley GU15 2PL UK http://www.concoat.co.uk
>>
>> Application Engineers in Chemical Compounds to the Electronics Industry
>>
>
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