Formatting as plain text and posting for Kris Roberson:



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Hello TechNet-ers



The IPC-AJ-820 committee is requesting information on some equations in the new revision.



The following is from section 9-29-19 in the balloted “A” revision of the AJ-820:



“9.19.29 Simplified Strength Calculations PTH calculations:



The solder strength is most easily calculated by dividing it into three sections: the solder side fillet, the component side fillet, and the solder in the hole, calculating the strength of each and adding them up. With a force on the lead in the component side direction, all sections of the solder will be under shearing force. The solder area in the hole will be: 



Area = Wire Diameter x π x Hole Length   Eq. 4-2



The solder area in each of the fillets will be:



Area = Hole Diameter x π x Smallest Cross Section               Eq. 4-3



The smallest cross section is the shortest distance between the edge of the hole and the top of the fillet. The following values will be used for the calculation:



Hole length                                                            1.52 mm

Wire diameter                                                        0.76 mm

Hole diameter                                                        1.02 mm

Smallest cross section (top side)                        0.l8 mm

Smallest cross section (bottom side)                 0.36 mm

Shear strength of solder                                       37.2 MPa



The strength of the solder in the hole is: (0.76 mm)(π)(1.52 mm)(37.2 MPa) = 135.4 N (newtons)



The strength of the solder source side fillet is: (1.02 mm)( π)(0.36 mm)(37.2 MPa) = 42.2 N



The strength of the top side fillet is: (1.02 mm)( π)(0.18 mm)(37.2 MPa) = 20.9 N



The total solder strength is:  135.4 N + 42.2 N + 20.9 N = 198.5 N



The peel strength of the top side land is: (2.54 mm)(π)(68.9 KPa) = 13.8 N



The peel strength of the barrel of the hole is: (1.02 mm)( π)(20.67 KPa) = 1.8 N



With the force pulling in the component direction, the solder side fillet will add strength without loading the copper-board bond. The strength, due to the laminated copper and the bottom side fillet is then: 13.8 N + 1.8 N + 42.2 N = 57.8 N

The amount of upward force on the lead the connection can withstand before breaking is 57.8. The actual damage threshold would be lower than this figure.”





In question are the underlined lines containing the KPa values for the Peel Strength (68.9 KPa and 20.67 KPa).



These equations were in the original publication but there’s no explanation as to the origin of the values.



How were these numbers derived?



If you have information leading to the resolution of this question you will have the gratitude of the entire IPC-AJ-820 committee.



Mr. Kris Roberson

IPC- Association Connecting Electronics Industries

Manager, Assembly Technology

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Phone: 847-597-2846

Fax: 847-615-5646

www.ipc.org







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