I have worked with various Pb-Free solders, primarily with solder paste and
wire for hand soldering applications.
Here are my conclusions when compared to SnPb:
1. Pb-Free solder joints have a more grainy appearance than their SnPb
counterparts.
2. Pb-Free solder joints are not as bright as their SnPb counterparts. They
can be considered dull in appearance.
3. Pb-Free solder does not wet as well as SnPb. In reflow soldering
applications, Nitrogen has been used to improve solder wetting. In addition,
the board and component finish does make a difference. OSP yields poor
results while Immersion Sn and NiAu yield positive results.
4. For hand soldering applications, using a strong flux with Pb-Free solders
will yield better results, but this causes problems with flux removal and
cleaning.
If you follow the IPC specifications on solder joint appearance, there is a
possibility that Pb-Free solders will not pass the current specifications.
In addition, even if they do pass the current specifications, operators /
inspectors will have to be "retrained" on what a good solder joint looks
like.
How these observations effect solder joint reliability remains to be seen. I
agree with Gordon, especially considering the solder joint requirements of
aerospace, DoD, and space are much more demanding than many of the Pb-Free
reliability tests.
I recommend getting color photographs of the solder joints to make the
comparison between SnPb and Pb-Free.
Lee Whiteman
Senior Manufacturing Engineer
ACI / EMPF
Telephone: (610) 362-1200; Ext. 208
FAX: (610) 362-1290
E-Mail: [log in to unmask] <mailto:[log in to unmask]>
> -----Original Message-----
> From: Leadfree [mailto:[log in to unmask]]On Behalf Of Corbel, Gwenna
> Sent: Wednesday, August 02, 2000 4:33 AM
> To: [log in to unmask]
> Subject: Re: [LF] Solder appearance
>
>
> Gordon,
>
> have you notice the grainy aspect you talk about with the lead free solder
> pastes ?
>
> -----Message d'origine-----
> De: Davy, Gordon [mailto:[log in to unmask]]
> Date: mardi 1 août 2000 18:10
> À: [log in to unmask]
> Objet: [LF] Solder appearance
>
>
> A question has been raised about the appearance of solder alloys
> other than
> eutectic SnPb and whether non-shiny is acceptable. The terms "dull" and
> "grainy" were used. Allow me to quote from J-STD-001 (para. 9.2.4).
>
> There are solder alloy compositions, component lead and terminal
> finishes, or printed board platings and special solder processes
> (e.g., slow
> cooling with large mass PWBs) that may produce dull, matte, gray,
> or grainy
> appearing solders that are normal for the material or process involved.
> These solder joints are acceptable.
>
> The surface of a solder connection has three visual attributes: luster,
> texture, and contour. The first two have to do with composition
> and cooling
> rate; the third with wetting. Except for those compositions that
> are at risk
> of lifting (as discussed recently in this forum), wetting is the primary
> reliability concern.
>
> Gordon Davy
> Northrop Grumman ESSS
> Baltimore, MD
> [log in to unmask]
> 410-993-7399
>
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