Eagle IC packages

Thread Starter

jpanhalt

Joined Jan 18, 2008
7,699
There is a small difference between packages that are nominally the same in Eagle.

To take just one example, if one compares the SO-08 package from Linear with the SO-08 from Maxim, the Maxim package is a little wider and the pads are a little bigger. Is there a "correct" version?

While on this topic, what is the difference between 8-pin versions of SOIC, SOP (used by Fairchild for LM555), and SO-08 (used by Harris and others for the identical chip)?

Thanks. John
 

SgtWookie

Joined Jul 17, 2007
22,201
I Googled:
http://www.google.com/search?hl=en&q=SOIC+package+dimensions
and got quite a few hits on various manufacturer's sites, including a brief Wikipedia article.
http://en.wikipedia.org/wiki/Small-Outline_Integrated_Circuit

Many of the library items in the Eagle Layout Editor were contributed by users. Not surprisingly, I have found a number of mistakes.

However, using "just one" pad layout for a particular package may be a mistake. For example, one SO-08 might be a power regulator, requiring large pads to dissipate heat; another SO-08 might be for a digital IC that requires small pads due to signal/bus routing between the pads. So, what is "proper" and "correct" for a given "standard" package configuration is subjective.
 

Thread Starter

jpanhalt

Joined Jan 18, 2008
7,699
Thanks for the response.

Here is part of the answer I found on further searching.

Dallas/Maxim (maybe some others) use a 208-mil wide SOIC. It is not common. The common ones are 150 and 300 mil. In fact, the Eagle version I have doesn't show that size for any Maxim, Linear, TI, and a few other manufacturers that I checked. It may be there, but it's well hidden. I guess I will have to draw it, but obviously, I will have to play with the grid size to get it right.

There are several sections in Wikipedia related to my question that I searched first before posting and at least one error in which the SOP was referred to as a 0.025 pin spacing. There is also a very common 0.05 spacing (same as SOIC). While Wikipedia is a great resource for fast answers, and it is mostly correct, I tend to go to the sources when it matters. Here are two useful sites for size information:
http://www.maxim-ic.com/design/manufacturing.cfm
http://www.analog.com/Analog_Root/Packages/Packages_Home/

As for the other part of the question, I tend to use only CadSoft libraries. The Linear chip (SO-08) did not have a orientation mark and its pads were slightly narrower than the Maxim and others for the same package. I assume that was due to different engineers/draftsmen at CadSoft. I prefer the slightly wider pads, as the chip tends to slid off the narrower pads during soldering. (That was something I noticed using the Linear packages prior to today, but didn't realize there was a different package available.) I have now fixed the orientation mark, but will keep two versions of the package, just in case I ever try to run a signal between the pads.

John
 

hgmjr

Joined Jan 28, 2005
9,029
I have found that the best bet is to use the Eagle Part editor to design your own land patterns. Then you will not be dependent on someone elses determination of the ideal pad sizes.

hgmjr
 

scubasteve_911

Joined Dec 27, 2007
1,202
There are various versions of nearly every package! You must make sure that your footprint/landpattern matches the device via checking the datasheet's drawing.

In my software, there are about 10 different versions of each basic type :)

Steve
 

Thread Starter

jpanhalt

Joined Jan 18, 2008
7,699
Thanks for the heads-up. I had assumed that an SO-08/SOIC-8 would be the same size regardless of who made it, just like the standards we have for bolt threads. Fortunately, I discovered in time that the SOIC-8 from Maxim for its digital pot (DS1869, 208 mil) would not fit the same pattern as the SOIC-8 from Fairchild/Linear for the LM393 (150 mil). In the future, I will pay better attention to the package part of the datasheet. John
 
Top