[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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