Steve,
     
     Where can I find the information that supports the barrel fill 
     strength as compared to the lead ? Was there a paper written ?
     
     Thanks for the response.
     
     Darrell Drake
     SSDS
     Houston, Tx.
     


______________________________ Reply Separator _________________________________
Subject: Re: DES:ASSY: component mounting
Author:  [log in to unmask] at Internet-Mail
Date:    5/30/96 11:03 PM


>Message was resent -- Original recipients were: 
To:
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--------------
[log in to unmask] asked ............ 
>     
>     To all,
>     
>     In reference to IPC-D-275 Section 4.2.1.2 Clinched Leads (Type 1) the 
third 
>     paragraph states "Type 1 is not applicable to leads of dual-inline 
packages 
>     (DIPs)...." Q
>     
>     Question: What are the technical reasons why Type 1 clinching is not 
>     considered applicable for DIP packages ?  
>     
     
....................Another reason, from personal experience, is that the 
stiff steel leads of DIPS, require large amounts of force to bend to a full 
clinch.  The pressure exerted against the knee of the PTH can cause lifted 
pads or damaged barrels, including tearing of the copper.  Inward is worse 
than outward because of the extra force required to overcome the natural 
outward bend of the lead.
     
>     We have a customer who has designed a Class 3 board where all DIP 
packages 
>     (as well as all pins for each DIP) are PTH with full clinch pads, the 
>     clinch is towards the body. 
>     
>     Are there mechanical advantages to this method ? 
     
No....If your leads meet solderability requirements, the solder in the PTH 
is far stronger than the lead. 
     
>     
>     What are the disadvantages ?
     
Full clinch partially blocks the PTH, possibly causing soldering defects. 
Also major rework hassle...
     
>     
>     This board is subject to both high temperature and high vibration.
     
If the only way the designer could think of to make his design resistant to 
temp and vibe was full clinch, somebody ought to forceanly drag him from the 
sixties into the nineties.  Full clinch is a holdover from single and double 
sided boards without PTHs.  If I recall the number, a stud joint with a full 
barrel fill and top and bottom solder fillet is about seven times stronger 
than the lead.  This sounds like another of those legacy requirements 
started by an incident at your customer's facility many years ago.  I would 
suggest wooden stakes and silver bullets.
     
Good Luck
Steve Mikell
SCI Systems
Huntsville, AL
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Steve Mikell, Process Engineer, Soldering & cleaning processes 
SCI Systems Plant 13
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