90% is by weight so you can't use that figure, by volume it's 
approximately 50% for most solder pastes.

You'll only need approxiations for this purpose anyway so to use the 
aperture area (including reduction) x stencil thickness divided by 2 will 
give you a useful figure for solder volume.

Grunde




"Nowland, Russell Howard (Russell)" <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
20.05.2008 18:40
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Re: [TN] Average paste volume estimate






Well,

We did a study many years ago and I need Greg Munie see if he remember
the results.  We actually did it on a PCA basis where we weight the bare
PWB, PWB with paste and post reflow.  We were trying to determine from
that the volume of tin/lead.

You can take the area times the stencil thickness plus one mil (if you
are using metal squeegee blades).  That will give you the average paste
volume.  Then you will have to look at the percent of metals in your
paste. The % metals for the Indium SMQ92J is 90.25% but will vary from
paste to paste.  Then if you can identify the weight of Sn/Pb you can at
least ballpark the number of grams per PCA.

Perhaps Greg has more specific info.  He is part of the TechNet but I
sent it directly to him also.  Good luck

Russell Nowland
Alcatel-Lucent 
Advanced Manufacturing Engineer
Address: 14000 Quail Spring Parkway, Suite 300
Oklahoma City, OK 73134
email: [log in to unmask]
Desk: 405-302-1660
Cell: 405-203-0034
Fax: 405-302-1622
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Tuesday, May 20, 2008 11:23 AM
To: [log in to unmask]
Subject: Re: [TN] Average paste volume estimate

It depends.

The smaller the aperture, the less paste left on the board.
The thicker the stencil the less paste left on the board.
And then you have your aperture ratio that combines the two.
And then there is which specific paste you are talking about.
Etc., etc.

I would say to be safe - between 0 and 100%.  But I think we can say it
is usually between 30 and 90%.  I am a lab rat, so process engineers may
be able to refine this a bit.

Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dan Mathews
Sent: Tuesday, May 20, 2008 12:10 PM
To: [log in to unmask]
Subject: [TN] Average paste volume estimate

 Does anyone have an easy way to estimate how much paste is applied to a
smt pcb? I understand it varies on 

squeegee pressure, stencil thickness, and pitch of the components but I
was looking for an average. I would

assume that somewhere out there someone can estimate that "2 grams of
paste is used on a 2" x 2" smt pcb". 

 

 I will then use this information to determine how much lead is used on
non-RoHS products due to solder paste 

issues and not non-compliant components. 

 

Thank You in Advance,

Dan

 

Dan Mathews C.I.D.+

Engineering Support Supervisor

B&B Electronics

Ottawa, IL USA 61350

Phone: 815-433-5100 ext 217

Fax: 815-434-8831 (direct to my desk)

URL: http://www.bb-elec.com <http://www.bb-elec.com/> 

 

 

 


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