The grainy condition is something I have seen several times on very high-mass
boards.  If the solder cools very slowly, there is condition developing
inside of the solder where the lead and tin are solidifying at slightly
different times.  The lead particles or dendrites are forming small pockets
of solid lead that then are surrounded by liquid tin. This causes the solder
joints to appear as if they have sand stirred in prior to cooling.  This
condition looks very much the same as overheated solder, but does not have
the discoloration and dewetting that are commonly seen on overheated joints.
The "cracked ice" condition is a very similar phenomenon of joints that cool
slowly.  The liquid solder does "skin-over" while the inside is still liquid,
then develops the lines or "cracks" as the inside solidifies.  These
conditions both occurring on the same board indicate to me that a high-mass,
slow cooling cause is the most likely, with the grainy appearance probably
being on the joints that cooled the slowest of all.

Jon Moore

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------