IPC Land Calculator help

[kungfucharlie]

I am new to pcb design and the IPC-SM-782A standard so please bear with me. I am trying to learn how to use the IPC's online calculator have but am not sure I am getting the right results. As a reference, I used the registered land pattern 300A component dimensions, a fabrication and placement tolerance of .1, toe solder fillet of 0.8, heal solder fillet of .5, side solder fillet of .05, Z adj of 0, X adj of 0 and a G adj of 0 and did not get results that match RLP300A. I even used the nominal toe, heal and side fillets and it still did not get results that matched the RLP300A. Should I be doing something with the Z, X, and G adjust? Please help guide me in the right path since this is such an important part of pcb design. Thanks.

Sincerely,

Kirk Morris

PS.

Here are the component dimensions for RLP300A form IPC-SM-782A section 9.1 page 2.

Lmin: 5.80
Lmax: 6.20
Wmin: 0.33
Wmax : 0.51
Tmin: 0.40
Tmax: 1.27
Amin: 3.80
Amax: 4.0
Bmin: 4.80
Bmax: 5.0
Hmin: 1.35
Hmax: 1.75
Pnom: 1.27

[Tom]

Kirk,

I know exactly what you are referring to. You enter all the correct numbers into the calculator (even if you get the numbers right out of the IPC-SM-782 book) and the calculator land pattern results differ from the 782 book. I talked to IPC (Dieter Bergman & Gary Ferrari) about this and they are aware of the issue. Basically, Dieter Bergman has studied each and every landpattern and he personally is the mastermind behind the final dimensional data of each pattern. He has the final say-so. Unfortunately we cannot take Dieter's brain and put it in a calculator, nor can we make a calculator output data that Dieter concludes is the best for each pattern. And it's extremely difficult to create mathematical formulas that apply to every group or family of parts.

Right now IPC is in the process of updating the land pattern calculator to the new 3-Tier system (Least, Nominal & Maximum conditions) that pcbstandards.com currently uses. It will be on-line sometime this year. In the meantime I recommend that you download our landpattern calculator and give it a try.
http://www.pcbstandards.org/downloads/Metric%20Environment/Calculators/Landpattern/

If you have any questions you'd like to me to personally give Dieter Bergman send them to me at - Tom.Hausher@WindRiver.com and I will pass them on to him this Wednesday when I'll see him again. (He's here in San Diego giving the 2nd IPC Advanced Certification Exam) I will post his reply here for you.

IPC and pcbstandards.com are working together to create a "One World Library" using metric units that is available to the world for free. Someday we will get there.

[Mark Larson]

In the back of each component section there is some information on toe and heel, if you read it you will see that this info can be used for an alternate decal to the IPC recommended decal. I have used this data to develop footprints. A long time ago the rule of thumb was a good solder joint has a fillet that forms an angle between the edge of the pad and the top of the lead at between 30 and 60 degrees. So I always shot for 45 degrees to hit between these extremes. If you notice the data in each section shows max and min for fillets, in using a number half way between the max and min I found it closely matches the 45 degree rule. As a bonus the resulting land pattern always takes a little less space than the IPC recommended one. My conclusion is that the old 30/60 rule is still valid and if you want a simplified formula for developing footprints go ahead and use it.