One guess as to why they are cracking is that when pasting the 2nd side, it is possible that the supports that come in contact with the bottom (1st pass) parts are hitting the SOT's and exposing them to excessive force.  A crack may or may not be caused at that point, but will certainly become evident after going thru a thermal event such as the reflow oven.



-----Original Message-----
From: Virgil Lenton [mailto:[log in to unmask]]
Sent: Thursday, January 16, 2003 1:43 PM
To: [log in to unmask]
Subject: Re: [TN] Cracking SOT-23


I apologize for the vagueness in my original posting.
This is what we know so far about this problem.

- It does not appear to be Z-height related - nozzles are spring loaded and
we have double checked.
- Breaks are complete breaks through the center of the body. Sometimes
the 'lid' comes off, but most often they crack top to bottom right through.
- We have *not* explored the possibility of moisture, but at this pont we
feel moisture is unlikely.
- The components in question are all placed on pass 1. We havent yet
checked to see if they are cracked before pass 2.
- It is not always the same part, but always SOT-23.
- The profile used is our 'standard' profile that has been used for about 3
years.

Regards
Virgil

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