To263-5

[bbpcb]

In the handbook file 06_TOs.pdf for the TO-263NS-5N ( National )how did you obtained / calculated the quote for T1(1.35mm) and T2(10.20mm)?
In the National TS5B package datasheet T1 is 1.9mm and there is not indication about T2.
Thanks

[Tom]

The National Semiconductor datasheet is very vague at providing the necessary information to build the exact land pattern. The "T1 & T2" dimensions are not really accurately provided. (At least in the datasheet that we have).

We studied National Semiconductors "Recommended Land Pattern" and calculated backwards. Since National did not provide the adequate physical dimensions, our land pattern closely resembles the National "Lead Position Overlay", which we have used on real high volume PCB designs that produced good results.

[coreya]

I am starting to hate TO-263 packages, since no two are alike. Our CAD person is balking at using the landpattern calculator for a SEMTECH EZ1086 in TO-263 package and wants to use the landpattern given in the datasheet (attached), because neither the JEDEC TO-263 specification nor the EZ1066 datasheet gives T2. The CAD person also thinks that the pin pads are unnecessarily narrow. I measured T2 on an actual part (T2=7.88) but she was still unhappy with the results.

I am trying to come up with a standard landpattern development method in hopes that parts from different manufacturers might use that same landpattern. We try to determine if a package is close to a JEDEC outline, and use those numbers in your calculator. Unfortunately, the calculator wants dimensions not in the JEDEC specification. The SEMTECH part seems to follow the JEDEC TO-263 specification more than the MO169 standard.

I how should I approach the CAD person resistance to the calculator?

[Tom]

Just got back from Toronto, so sorry for the late response.

I agree that TO-263 packages are painful because the manufacturers are too vague in their component dimensional data. It almost makes it impossible to use the landpattern calculator for this particular component family.

So, I would highly recommend that you use the exact land pattern that SEMTECH provides. Also, if you could e-mail me the SEMTECH PDF file, I will investigate (evaluate) their recommendation and add that specific part to our standard documentation.

[coreya]

Tom,

I attempted to attach the datasheet last time, but it appears to be outside my skill level. I’ll try again. If I fail again, I’ll email you the file. I have added the calculator output to the back of the datasheet. I measured T2 for a part and added a little for MAX. The SEMTECH pattern has very wide pads as compared to the calculator’s. Are there any ramifications for wide pads – good, bad, or indifference?

The CAD designer was confused by the “+” mark in the drawing which C1 and C2 are referenced. I told the designer the “+” was the part center, toe to tab. C1 and C2 were to the center of their respective pad. I hope this was correct. Is there a document that describes the drawings?

Thanks

Corey

[Tom]

OK, The new TO-263ST-3N is built and the documentation has been updated. Send me an e-mail and I will send you the updated data.