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September 1997

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Subject:
From:
"Mark W. Spitnale" <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Tue, 2 Sep 1997 09:42:04 -0500
Content-Type:
text/plain
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text/plain (48 lines)
I believe the dewetting and tombstoning issue can be influenced by component
placement. If the part is off placement to far when the solder reflows on
the pad termination, it can either lift the part (fulcrum action) on one end
just high enough that it looses contact with the solder on the other end or
tombstone.  Keep in ming that due to the mis-placement the one termination
was not / may not have been in contact with the paste to hold it down to the
pad.

Similar situations can be found on parts such as QFP or SOIC which have
lifted /bent lead.  The inspector may classify the defect as "dewetted"
where in reality the part recieved little flux and solder contact due to the
lead being lifted.  The "lead" is actually very solderable if the solder
/paste is appropriately applied.  However, this is very difficult when the
lead is bent up in the air.

*****SNIP
>>
>>Hi Technetters,
>>
>>Could anyone give me some advise on the dewetting issue.
>>
>>One of our component supplier told me that misalignment of the chip
>>component will cause dewetting.
>>
>>I haven't heard of such thing before, and couldn't believe so. However, I
>>would like to hear from others' opinion about this issue, whether this is
>>of a true statement from my suppiler, stating "Dewetting can be caused by
>>Misaligment".
>>
>>
>----------------------------------
>Jeff L. Hempton        phone: (219) 429-7335   Fax: (219) 429-4688
>Boardshop Manufacturing Engineer                       Mail Stop: 25-31
>Hughes Defense Communications
>1010 Production Road, Fort Wayne, IN 46808-4106
>Email: [log in to unmask]
>
>"The man who rolls up his sleeves seldom loses his shirt."--Thomas Cowan
>
>
>
----------------------------------
Mark W. Spitnale                Phone: (219) 429-5992   Fax: (219) 429-4688
Hughes Defense Communications                           Mail Stop: 25-31
1010 Production Road, Fort Wayne, IN 46808-4106
Email: [log in to unmask]


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