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March 2003

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Wed, 19 Mar 2003 07:55:03 -0500
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ENIG is harder than HASL and thinner than HASL.  When you apply force to
the contact, I believe HASL is better due to its capability to deform
and comply to the surface of the contact.  In addition, if you heat up,
the solder will creep under pressure, form better contact interface.
The underlying metallization if Ni for ENIG, it is harder material and
can not be deformed easily upon force.  Plus the dis-similar metal
contact etc.etc.
My 2 cents.
                                                   jk

>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Hillman
>Sent: Tuesday, March 18, 2003 8:47 AM
>To: [log in to unmask]
>Subject: Re: [TN] Heat transfer from ENIG board to aluminium casing
>
>
>Hi folks! Let's look at some numbers! The thermal conductivity
>(in W/ m K in the 0-100C range) is 237 for Al, 318 for Au and
>66.8 for Sn. You should have better heat transfer by going way
>from Sn - but as Brian described the thermal transfer game is
>ruled by surface contact. Brian also mentioned the
>issue/question of galvanic compatibility, the same question  I
>queried the TechNet community on several weeks back. I
>received a number of good information leads but nothing as
>definitive as I was looking to obtain. Here is an update to
>that question - I began a series of tests: the silver/aluminum
>and gold/aluminum galvanic couples test vehicles (circuit
>boards with the appropriate finishes coupled to Al casings by
>Al standoffs and having a 5 volt bias) have completed 250
>hours of 85C/85%RH with no issues of galvanic compatibility!
>The salt fog tests begin next week and I'll keep everyone
>updated as those tests progress. It appears that the
>anode-to-cathode relationship is a key parameter in equation.
>
>Dave Hillman
>Rockwell Collins
>[log in to unmask]
>
>
>
>                      Brian Ellis
>                      <b_ellis@PROTONIQ        To:
>[log in to unmask]
>                      UE.COM>                  cc:
>                      Sent by: TechNet         Subject:  Re:
>[TN] Heat transfer from ENIG board to aluminium casing
>                      <[log in to unmask]>
>
>
>                      03/18/2003 06:54
>                      AM
>                      Please respond to
>                      "TechNet E-Mail
>                      Forum."; Please
>                      respond to Brian
>                      Ellis
>
>
>
>
>
>
>Daan
>
>I would have thought exactly the opposite! An uneven HASL
>surface will have fewer contact points to the aluminium than a
>flat ENIG surface. That having been said, I would have thought
>that both would be bad, electrochemically speaking, if
>subjected to humidity. From very poor memory, the Al-Au couple
>is somewhere about 4 V, roughly double that of Al-Sn/Pb.
>
>Brian
>
>d. terstegge wrote:
>> Hi Technet,
>>
>> We are in the process of converting some of our boarddesigns
>from HASL
>> to ENIG conductor finishing. Now one of our designers is
>worried about
>> the effect that this change may have on heat transfer from
>the plated
>> board-edges to the aluminium casing on which the board is
>mounted. He
>> feels that the heattransfer from leadtin to aluminium is better that
>> for nickel/gold to aluminium, possibly resulting in heat problems in
>> the end product.
>>
>> Any ideas on this ?
>>
>> Daan Terstegge
>> Thales Communications
>> Unclassified mail
>> Personal Website: http://www.smtinfo.net
>>
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