Some extracts of the article pointed out by Steve are below. Thicker
is better as far as joint fatigue, which makes sense. Copper is not as
flexible as solder.
Ramon
> Information on how the ramp time, hold time, frequency, and temperature
> affect the fatigue life of solder joints has been studied and published
> [Vayman]. However, information on how the height of the solder joints
> affects the fatigue life of surface mount solder joints is not readily
> available.
> This solder joint fatigue problem presented an interesting question.
> Should the solder joints be reworked to increase solder joint thickness
> and lengthen the fatigue life? Several engineers had conflicting points of
> view on how the height of the solder would affect the fatigue life.
> The NASA hand soldering requirements in NHB5300.4 (3A-2) indicate that,
> for lapped solder joints, the maximum distance between the foot of the
> lead and the termination is .010 inch.
> Solving for Stress and Strain Values. The finite element analysis code,
> ABAQUS, was used to solve the mathematical model of the SOT23 package. The
> results of the analysis are depicted in Table 1 and Figure 2. FEA showed
> that increasing the thickness of the solder joint did not affect the
> overall stress values on the SOT23 package as a whole. However, it did
> show that the strain values on the solder joint were affected by changing
> the thickness of the solder.
> FEA showed that increasing the solder joint height may have a favorable
> effect on the solder joint's fatigue life. As a direct result of
> increasing the thickness of the solder joint, the plastic strain in the
> solder was reduced. The fatigue life of the solder joint doubled from 28.5
> cycles at 2 mils to 59.2 at 10 mils. Our results show that below 4 mils,
> the solder joint was subject to cyclic failure much sooner. After 4 mils,
> the number of cycles increased with thickness, but not as drastically as
> it did from 2 to 4 mils. This is evident in Figure 3.
>
>
> -----Original Message-----
> From: Steve Gregory [SMTP:[log in to unmask]]
> Sent: Wednesday, October 01, 2003 4:56 PM
> To: [log in to unmask]
> Subject: Re: [TN] Reliability solder
>
> Hi Paul!
>
> To answer your question; Is water wet? Does a bear poop in the woods?
> (GRIN)
>
> After careful consideration, one would have to answer in the affirmative
> to both scenarios posed above. So the short answer to your query is;
> "uh-huh"...go to:
>
> http://nepp.nasa.gov/eeelinks/vol_01/no_02/eee1-2d.html
>
> Here you will find a summary of a report done by Hyun Soo Park of NASA,
> "Theoretical Analysis to Determine how Solder Joint Height Affects the
> Fatigue Life of the Solder Joint". It also has a list of references that
> include no other than our own Technetter guru; Werner Engelmaier, of all
> the work that's been done in this area.
>
> -Steve Gregory-
>
>
>
>
>
>
>
>
>
>
> Paul Stolar
> Materials Engineer
> Houston Technology Center
> Baker Atlas
> 713-625-5376
> 713-625-4949 (fax)
>
>
>
>
>
> Has anyone ever done any experiments to determine the effect the
> solder
> thickness under a lead has on the joint's reliability?
>
> Paul Stolar
> Materials Engineer
> Houston Technology Center
> Baker Atlas
> 713-625-5376
> 713-625-4949 (fax)
>
>
>
>
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