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Subject:
From:
Torsten Hagge <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Torsten Hagge <[log in to unmask]>
Date:
Thu, 17 Feb 2011 15:35:43 +0100
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Hi Cedric,

to solder such components nearly void free I suggest to use a vacuum vapour phase soldering system. 

On standard PCBs we run automotive products with low void paste, which is solder paste with less flux, through reflow. The paste reduce the void rate about 10%, additional nitrogen (oxygen less than 100ppm during lead free reflow) can reduce by additional 10% to nearly 5% void rate.

Best regards,
Torsten  

i.A. Dipl.Ing.(FH)Torsten Hagge
tech. projectmanager
Kristronics GmbH
Gewerbegrund 5 - 9
24955 Harrislee
 
Tel.:    +49 461 7741 624
Fax:     +49 461 7741 642
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www.kristronics.de
 
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-----Ursprüngliche Nachricht-----
Von: TechNet [mailto:[log in to unmask]] Im Auftrag von Cedric ORAIN
Gesendet: Donnerstag, 17. Februar 2011 15:26
An: [log in to unmask]
Betreff: [TN] Voids issue on Aluminium base plate

Dear Technetters,

We have to solder a RF power transistor onto an aluminium base plate and we
are facing with a very challenging issue.

We encountered a high voids rate (>30% or 40%) underneath the component body
(which is about 35x10mm). This is not acceptable for this application.

The component is Nickel/gold plated whereas the aluminium baseplate is
plated with Nickel and Silver and then cleaned with solvent.

We tried to change/adapt:
- soak time of the profile, 
- 2 difference solder pastes (SAC305), 
- change the screen design and thickness

Finally none of these parameters looks to have significant effect on voids
rate. We are now wondering if the solderability of the Ni/Ag plating is good
enough and even if it is convenient for that purpose.

Is somebody could give us advises? How to enhanced NiAg plating
solderability (acid ?!, ...)? Which flux could help to compensate the poor
wettability? Which kind of plating would be preferable? ...

Thanks and regards,

Cedric



-----Message d'origine-----
De : TechNet [mailto:[log in to unmask]] De la part de Douglas Pauls
Envoyé : jeudi 17 février 2011 14:07
À : [log in to unmask]
Objet : Re: [TN] Electrical Clearance as stated in IPC standards

Good morning Wee Mei,

IPC-T-50, the IPC "dictionary", lists the following:

Electrical Clearance:  The shortest distance between two conductors, which 
includes traces, terminals and structures, measured through the air.

IPC-T-50 does not contain terms for Clumpy, Trucklett, or Bobby 
Dazzler.....

Doug Pauls



Lum Wee Mei <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
02/16/2011 11:26 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Lum Wee Mei <[log in to unmask]>


To
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Subject
[TN] Electrical Clearance as stated in IPC standards






Dear All,
 
Until now, I am still very curious about this term "electrical clearance" 
that is used on the IPC standards. Very often, the standard will says 
something like "it is acceptable as long as it meets the electrical 
clearance". As I did not have the IPC standards with me when I right this, 
allow me to use a scenario to illustrate my query :
 
A digital PCB has some pockets of power and ground area fills with minimum 
trace width/clearance of say 6mil/6mil (0.15mm/0.15mm) and power trace 
width of 50mil. During bare board inspection (Class 3 requirement), one of 
the power trace that run along side of the ground fill, has an excessive 
copper protrusion that reduce the physical conductor to conductor 
clearance by 60%. Based on the IPC-A-600, it has violate the conductor to 
conductor clearance. However, the argument kick-in that it is not a 
violation and can be acceptable because the remaining clearance of 40% is 
much larger than the electrical clearance stated in IPC-2221 for that 
application. Now, how should this be resolved?
 
Thanks and Regards,
~ Wee Mei ~

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