Yes, very true. I have seen some fab docs actually have an arrow showing the
direction of the squeegee when applying the paste.

Screen opening that are rectangular will get good paste if parallel to the
squeegee flow but not so good if perpendicular. This is really for small
openings such as 0.015" wide x 0.100" long. The 0.015" wide slot, if
squeegeed perpendicular, gets very little paste.....

I have that problem on a design now. After reflow, 1 part has to get touched
up by hand, which is bad for quality overall....

Regards
TDK




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Le Thanh Tung
Sent: Tuesday, May 10, 2005 6:39 PM
To: [log in to unmask]
Subject: Re: [TN] Tombstone

Following is one of reasons cause Tombstone:
    - Vertial shifted part: Mounting condition is NG
    - Not same solder paste volume at two sides of part: Printing condition
is NG.
    - Temperature at two electrodes of part is different: when PCBA going
through reflow machine, one electrode
       of part will be heated and smell first -- > tombstone
Best regard.

----- Original Message -----
From: "Suganthi" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, May 10, 2005 2:51 PM
Subject: [TN] Tombstone



Dear All,

What is called Tombstone effect ,please explain me , and tell me how to
overcome this problem..

Thanks and Regards

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Suganthi

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