who do you call? (SML, SMN, and SMM?)

[ARGold]

Hi folks:

I am looking for a particular PCB decal in the pcbstandards library.

Please excuse me but I am just learning the structure of pcbstandards. I don't know who to ask how to find it the info, and maybe this thread will help others learn as well.

The land pattern I (think) I need is a QFPS7X7-48L.

From the L at the end, I think it should be in the Least Use Environment and so I looked in the Least Material Condition (SML) library. I didn't find any QFP's there.

There is, however a QFPS7X7-48N in the SMN library. Is that the part I want to use? I couldn't find a -N suffix part in the documentation so perhaps someone could point out the differences.

Thanks,

Allen Goldstein

[randychase]

The contact man on decals and part types is Tom H. He is the main coordinator for the libraries, though others are involved, so asking a general question here should work, specially as the other people come on line.

The N refers to the nominal library part as compared to the max or least parts. There are far more QFPs in the SMN library than there are in the SMM and SML.

Tom could speak more to this.

[ARGold]

It might help if I mention that the pitch is 0.50mm.

[ratkiller]

I've seen alot of 48 pin soic parts with a pin pitch of 50 mils

Why don't you build the part. Get the Mechanical from your engeneer and build the decal. It's a pain but once it is done it is done.

Maybe you meant some thing else. Just trying to help.

[randychase]

I think it finally clicked on what the issue is.
QFPS7X7-48L is the part number, but the L means something else in your part.

All the parts that are in L, N, and M are the same lead pitch. Basically it's the implementation of a three tier library system that is being created. The idea is that you typically use the N (Nominal) series parts for most boards. The M (Maximum) part is used on designs that need to be more robust. The L (Least) is a part decal that compromises a bit for space reasons. You can use the L, but it's not preferred and may affect your throughput.

So, a 7X7 QFP is the same 7X7 body regardless of L, N, or M, same lead spacing. If the N works for you, use it from the SMN library.

I hope that helps!

[ARGold]

Thanks Randy:

QFPS7X7-48L is the shape as shown on line 6 of the in the library document "L_QFPS5S.pdf" found in:

\Metric Environment\Library Documentation\Surface Mount\Least Material Condition

This shape matches the specs on the manufacturers data sheet for the part I am using.

There is *no* library document "N_QFPS5S.pdf" found in:

\Metric Environment\Library Documentation\Surface Mount\Normal Material Condition.

Yet there is a QFPS7X7-48N pcb decal in the SMN library while there is no QFPS7x7-48L decal in the SML library.

You are telling me that I *can* use the "-48N" PCB decal found in the SMN library, but I am interested if anyone can tell me if there is any physical difference between this decal and a possible decal for a "-48L" part which would match the specs found Least Material Condition documentation.

It always pays to be sure... (Good judgement comes from experience, experience comes from bad judgement.)

Thanks for the help.

-Allen

[ratkiller]

N L and M is that a particular manufactures standard, Randy or where you referring to an ipc standard?

My guess is Allen there would not be much of a difference. I would have to look at the mechanical to really tell.

[ARGold]

I think the documentation I am referring to is copied from an IPC standard, but I cant be sure.

You can have a look at those documents by following the paths I gave in the pcbstandards site index and tell me what you think.

-Allen

[Tom]

Allen,

The L, N & M are library suffixes in the naming convention. They refer to the environment use of the landpattern. There are three complexity levels in the pcbstandards surface mount library. A good resource for this is located on the Site Index/Technical Papers/Creating a CAD Library. You can contact me if you want the paper. It's 3 meg zipped.

Here is a brief description of the three complexity levels:

Maximum: Automotive, Aerospace, and Medical Applications. Anything that has high shock & vibration or life support characteristics or the need to be easily reworked due to the high manufacturing costs. These boards must have an on going component manufacturing supply line that is guaranteed by the component manufacturer to provide a 5 year supply of any and all components that are used on these boards.
The pad size and the placement courtyard for a maximum CAD library part would be robust.

Nominal: Consumer Devices, Computers, Appliances and Home Entertainment Systems. Average dependable Processor driven devices that pass drop tests and are not life support dependant. These boards would be reworkable if necessary, but the rework process is decided on the value of the product and the manpower labor to perform the rework. (Sometimes it's easier to throw the product out and buy a new one) These boards do not have a totally secure component availability. Some of the main parts may be available for at least 5 years but many of the "One of a kind" Maverick part could go out of business tomorrow.
The pad size and the placement courtyard for a maximum CAD library part would be average.

Least: Cell Phones, Toys, PCMCIA Cards and very Dense Boards. These are basically throwaway devices if and when they break or service to them is no longer provided. The component manufacturers basically "Make to order" many of the devices on these types of boards. Because of the mass quantity, boards must be made with minimum layer counts and custom components made exclusively for that particular device.
The pad size and the placement courtyard for a maximum CAD library part would be minimal.

[ARGold]

Thanks for your answer Tom:

I bought the CDROM, there is a paper called "Defining a CAD Library" is that the one you mean or is there another paper called "Creating a CAD Library which is not on the CDROM?

My original question was: would the QFPS7X7-48N decal work when the only documentation I can find in on the pcbstandards CDROM that matches the manufacturers dimensions for the part had a shape called QFPS7X7-48L.

From what I gathered, the N decal would work fine. I interperet your answer to tell me that there might be some small differences in solder pad dimensions, but the decal will work fine for the part.

FYI, the product I am designing product falls into the nominal catagory. But I think these catagories refer to intended uses of the individual parts themselves.

It might interest you to note that the document: SMTN_Index.doc has dead links to the QFP parts (and probably others).

[Tom]

Allen,

Yes, the Nominal library is what you are looking for. Typically all names of the parts in that library will end with a "N".

I researched all the links to the SMTN_Index.doc file on all the parts and I did not find any problems. This can only mean one thing, that you do not have all the PDF files in your directory that the Word file links to. When you get the CD-ROM, try it again and everything should work fine.

And you are correct, "Defining a CAD Library" is the technical paper that you are looking for. "Creating" was a typo.

Also, you can always e-mail me a PDF file of any part and I will tell you the decal name and the library it's in.

[jdupre]

>>My original question was: would the QFPS7X7-48N decal work when the only documentation I can find in on the pcbstandards CDROM that matches the manufacturers dimensions for the part had a shape called QFPS7X7-48L. <<

From what I have seen, the *component* dimensions for the Least, Nominal, and Maximum definitions are all identical for a given part. It is only the land pattern, assembly and courtyard dimensions that change. The L definition has the smallest real-estate usage and pads, the N is intermediate, and the M uses the largest amount of space and has the largest pads.

In the current library documentation the QFPS7x7-48 is listed in the N (nominal) land patern library. It is in the file "N_QFPS5S.pdf" which includes all square QFP parts with 0.5mm lead pitch. The component dimensions should match your part.

-Joe

[Tom]

Joe,

To answer your question correctly I need to give you some background information.

IPC-SM-782 profiles (illustrates) optimal component dimensions and "lead span - L1 & L2" dimensions for standard QFP packages and their related Land Patterns. The name of the Land Pattern is related to the Component Body, not the lead span. Example: QFP-14X20-100 = Quad Flat Package 14mm X 20mm "Package Body Size" with 100 pins.

Note: The gullwing leads of the QFP are soldered to the board (not the component body). So there is a danger involved when you assume that all manufacturers cut there "Lead Spans" the same length. Unfortunately they do not and this has caused major loss of waste in scrap material, time and money.

Some Component Manufacturers fabricate their QFP's using industry Standard Body Dimensions but mold and cut the Gullwing Leads at different lengths. Not knowing this, many PCB designers and engineers have mistakenly selected the incorrect Land Pattern.

An example of this is the QFP-14X20-100. In the SMN library there are five of these. There Land Pattern names are:
QFP-14X20-100N = IPC-SM-782 default Lead Span 17.2 x 23.2
QFP-14X20-100AN = Lead Span 17.8 x 23.8
QFP-14X20-100BN = Lead Span 17.9 x 23.9
QFP-14X20-100CN = Lead Span 16.0 x 22.1
QFP-14X20-100DN = Lead Span 18.8 x 24.8

Hence we have five different Land Patterns. Actually 15 when you introduce the 3-Tier system. Each of the five QFP's would have 3 different Land Patterns only in regards to the "Material Use". The only difference between Least, Nominal & Maximum Land Patterns are the Pad & Courtyard Sizes and locations. When the amount of Pad Heel & Toe change, so does the pin origins relationship with the part center.

Conclusion: You must look in the QFP Library Documentation and match ALL component dimensional numbers (including Height) to determine the correct Land Pattern name.

[Franco]

"Defining a CAD Library" found...
Will dive into it, thanks.

@ PCBstandards Team
PCBstandards is a great, sorry that I'm not a big help right now. This will change the more I use PADS instead of...