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Molded Body part cell

Printed From: PCB Libraries Forum
Category: Libraries
Forum Name: Footprints / Land Patterns
Forum Description: [General or a CAD specific issues / discussions]
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=417
Printed Date: 25 Nov 2024 at 4:39am


Topic: Molded Body part cell
Posted By: Nightwish
Subject: Molded Body part cell
Date Posted: 03 Jul 2012 at 6:45pm
I am using LP Wizard to create a Molded Body inductor and the setting for Side of pad is -0.1mm. The factory guys suggest that pad should be wider than the lead. I am not sure why LP Wizard uses this kind of settings. Please see picture below. I use level C when created the cell.
 
 
Thanks,
 
Nightwish


Replies:
Posted By: Tom H
Date Posted: 03 Jul 2012 at 6:53pm
This is the IPC-7351 standard. There is extra "pad width" generated by the Fabrication and Assembly Tolerances in the math. Sop when you use negative values for Side Goal you're only compensating for the other tolerances.
 
However, the LP Wizard User has full editing control of all the User Settings. Change the Molded Body Side Goal to 0.05 or any value the OEM wants.
 

Posted By: Nightwish
Date Posted: 03 Jul 2012 at 7:01pm
Hi Tom,
 
Thanks for your fast replySmile
 
I read the IPC7351 but can not find any words talking about this. Can you show me in which Chapter IPC7351 has a definition on this?
Also what is the benefit of this negative setting compared to a larger value? Or if there is other potential risk if we use a negative value during PCBA?
 
Thanks,
 
Nightwish

Posted By: Tom H
Date Posted: 03 Jul 2012 at 7:07pm
IPC-7351B Page 19 Table 3-13 "Inward Flat Ribbon L-Leads" (top of page)
(Molded Inductors, Diodes & Polarized Capacitors) 
  
Notice the Toe, Heel and Side Goals for "Nominal" environment and Side = -0.05
 

Posted By: Nightwish
Date Posted: 03 Jul 2012 at 7:14pm
Great!
 
I have IPC-7351A on hand and I found that table.
 
I will try to explain this to the factory guys and hope there is no big issue during PCA.
 

Posted By: Tom H
Date Posted: 04 Jul 2012 at 10:08am
IPC says there does not need to be a "Side Goal" for Molded Body packages because it doesn't do anything to improve the assembly attachment. i.e.: a side goal on Molded Body Inward L-Bend lead does nothing for the overall solder joint strength.
 
However, the Toe and Heel Goals are very robust for this component family and this is where the solder joint strength is. Also, not having a side goal aligns the package straight on the pads. If you add a side goal, the Molded Body part can drift during reflow and come out of the oven at an angle.
 
Think about it, the Inward L-Bend component lead is just a piece of formed sheet metal and what good would a side goal perform on a thin piece of sheet metal?
 
 
 

Posted By: Nightwish
Date Posted: 05 Jul 2012 at 5:08am
I confirmed this with our DFME and we made agreement that the cell is ok. Good news is the factory accept our librarySmile


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