Dave,

Here below is the sentence before and after. I don’t think the context helps at all.  But let me take a crack at interpretation myself, now that I have had a good night’s sleep.  Let’s assume the person is talking about the solder joint portion near the PCB pad. Laterally the tin-based solder is “seeing” the copper pad, which has a different CTE than the solder.  Vertically the solder is just seeing more solder which has the same CTE, so if the joint is going to crack, it is going to crack parallel to the PCB pad.  Do I, MOI make sense?  How would you rewrite the underlined sentence in question in quotes?

 

“For the reflow oven temperature profile, the thermomechanical response of the Sn content of the SAC305 alloy was considered.  As Sn is anisotropic, the size and orientation of the grain structure contributes to CTE mismatch fractures along the larger axis of a solder joint, laterally rather than vertically.  The grain of the Sn present in the solder joint grows during the reflow and continues to grow during the cooling.”

 

Regards,

Bev

 

From: David Hillman <[log in to unmask]> 
Sent: Friday, January 10, 2020 8:27 AM
To: TechNet E-Mail Forum <[log in to unmask]>; [log in to unmask]
Subject: Re: [External] [TN] Need interpretation

 

Hi Bev - the statement standing alone is out of context so it could mean a bunch of things. You would need to know the solder joint configuration and the what the X/Y/Z stress states to have the sentence make sense. I am assuming that the report from which the statement was taken would provide that information.

 

Dave Hillman

Collins Aerospace

[log in to unmask] <mailto:[log in to unmask]> 

 

On Thu, Jan 9, 2020 at 7:50 PM Bev Christian <[log in to unmask] <mailto:[log in to unmask]> > wrote:

TechNetters,



Can someone interpret this sentence for me?  

"As Sn is anisotropic, the size and orientation of the grain structure
contributes to CTE mismatch fractures along the larger axis of a solder
joint, laterally rather than vertically."



I know the following:

1.      Sn is anisotropic
2.      the size and orientation of the grain structure contributes to CTE
mismatch fractures

Is the latter part (.along the larger axis of a solder joint, laterally
rather than vertically.) always true and if so, why?  What am I missing?



Regards,

Bev