Carl,

You have seemingly got several enlightening and supportive messages from the
wisest of the wise. I have a comment too, not so rich in word as from guru
Stadem, but should be added to your collection. When you mentioned the look
of the gold, the following crossed my mind.  Gold seen by your eyes is not
what the microscope is seeing. The crystal size and the agglomeration of
crystals is many a times deciding what will be the joining result, either it
is wire bonding or glueing or soldering. Depending on the bath type, the
current or no current, the exposure time, metal additives etc the crystal
size varies from 100 A to 20,000 or more ! That has an impact on both the
wetting and the resulting solder joint. If you place 'cleanliness' as factor
number one for getting a good soldering, I'd put the the above as number
two.

I send to you offline three examples of gold microstructure, all with
different wettability and final solder properties. The images you get are
from electrodeposited gold, but all treatments behave likewise i.e. a
spectra of microstructures. I've pointed at this several times and wanted
microstructural properties implemented in the purchasing specifications, but
most of the involved groand and looked terrified.


Inge
On 19 September 2011 21:48, Carl VanWormer <[log in to unmask]> wrote:

> A surface mount PC board assembly (made by a local assembly house and
> passed by our outgoing test) was returned from the end user, along with
> an electrolytic capacitor that they had "knocked off" the board.  After
> looking at the assembly and component under a microscope, I noticed that
> the "gold plated" PC board (Lead free) had a fine granular solder
> appearance (much smaller grain than solder paste balls) on the pads
> newly exposed, with the whole "melted solder" blobs (in the shape of the
> pads) attached to the capacitor leads (with a similar granular
> appearance).  After minor scraping of various parts, I had come to no
> brilliant conclusions, so I pressed my finger nail against an inductor
> that was of similar size to the capacitor.  It popped off the board with
> the same symptoms as the capacitor.  After recovering from my surprise,
> I realized that I have no clue about the causes or cures for my
> component adhesion problem.  Can any of the more experienced members of
> this fine group direct me to some key words that might lead me to a
> quick education (and solution)?
>
>
>
> Thanks,
> Carl
>
>
>
>
>
>
>
> Carl Van Wormer, P.E., AE7GD
>
> Senior Hardware Engineer
>
> Cipher Systems
>
> 1800 NW 169th Place, Suite B-100
>
> Beaverton, OR  97006
>
> Cipher Systems (503) 617-7447 x 5163
>
> Direct Line (503) 425-5163
>
> [log in to unmask] <mailto:[log in to unmask]>
>
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