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 Post subject: Help a little shy
PostPosted: 26 Dec 2015, 20:35 
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Joined: 18 Dec 2015, 15:35
Posts: 162
Trying to use the Pattern Editor has been, lets say a learning experience. In the Pattern Template windows with Lines selected I have 2 lines of 4 pads, the pad spacing (PITCH I hope) is .65 but the line spacing, what can I say. Is this the spacing between the two lines of pads to:
1. the inside of the pads?
2. the outside?
3. the center?
After doing the math:
(BOSCH is TERRIBLE on drawings)
From the 'PACKAGE center line' to the inside of a pad is .755 with width of the pad with a vertical lines is .5 so the
INSIDE 1.55
OUTSIDE 2.55
CENTER 2.05

Plugging those number into the Line Spacing: box I end up with OUTSIDE being the Winner! This isn't talked about in your help nor is it explained why you decided on OUTSIDE, the one measurement that doesn't have to be close.
The INSIDE measurement HAS to be exact or damn close since it matches the physical pad of the device, the OUTSIDE pad, it can be ±.1 and should extend around .2. Since some manufactures do not provide recommended land patterns when figuring out what to build the INSIDE measurement is the starting place since center placement depends on the pads width which will change the placement.

I'm sure I'm missing something here, the other tools I've used have all three measurements, you enter the one from the drawing and the program calculates the others as you leave focus from your entry.


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 Post subject: Re: Help a little shy
PostPosted: 31 Dec 2015, 15:24 
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Joined: 20 Jun 2015, 14:39
Posts: 944
Not quite sure about all of your questions, but Pad Spacing and Line Spacing are referenced to pad origins (centers). Pad Width and Height are referenced to a pad's outline (outside dimensions). Does the following illustration help?...


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 Post subject: Re: Help a little shy
PostPosted: 02 Jan 2016, 14:22 
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Joined: 18 Dec 2015, 15:35
Posts: 162
I should have been a little clearer: BOSCH BMF055 https://ae-bst.resource.bosch.com/media ... 000_01.pdf They seem to like strange.

Weird QUAD with strange pin 1. They call it a Standard LGA I didn't think so since the horizontal and vertical pins were different sizes, I mean what standard is there that allows 'ANYTHING GOES'?
Seems they were right, 'ANYTHING GOES' is allowed.

After calculating the Inner, Outer and Center I realized I was 'DOING IT' again: Building a PCB pad using measurements for a device. After my da moment I moved on with the new problem, finding the center point based on a pad size with a fixed inner location.
The package is 5.2mm X 3.8mm with the pads all offset by .1mm: The vertical Inner = .1+(.375*2) - 5.2 = 4.25
The Center should be .375+.3 = .675/2=.3375*2+4.25 = 4.925

Your layout tool works well on PCB layouts but sometimes, more often then not, the manufacture leaves the heavy work to us by not providing recommended land patterns.
On this device I drew the land pattern with my CAD package and exported it, 2 minutes, when I was working on the package in diptrace my head exploded doing the math.



BOSCH does provide the land patterns for some of their devices but I think since Atmel made this device they are referring to Atmel, Atmel does not have a 28 pin device like this.

If there is a calculator hidden in DipTrace let me know or if there is another way to build a land pattern for the BOSCH device I'd like to know.
Thanks

FYI: The pads change sizes your tool doesn't allow that, all pads the same or one by one you can place strange pads, now I remember why I used the CAD system.


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 Post subject: Re: Help a little shy
PostPosted: 02 Jan 2016, 17:04 
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Joined: 20 Jun 2015, 14:39
Posts: 944
KevinA wrote:
Your layout tool works well on PCB layouts but sometimes...
I'm not affiliated with nor do I represent DipTrace. I'm only trying to give help on the forum based on my limited knowledge of the software. I have included a pattern library below named LGA-28.lib with my interpretation of the Bosch footprint you referenced. You're welcome to use it, but I cannot guarantee a proper fit or fireproofing as I have never tested it. Creating it was a bit of a challenge, but only because of Bosch's datasheet. Bosch's document shows the bottom view, so I have flipped it from left to right and numbered the pins accordingly.

KevinA wrote:
...The pads change sizes your tool doesn't allow that, all pads the same or one by one you can place strange pads...
Again, I'm not affiliated with nor do I represent DipTrace.

Resizing more than one pad at a time:
1) Select (highlight) the pads you want to resize.
2) Right-click on one of the highlighted pads and select Properties... in the pop-up menu.
3) Choose the Type / Dimensions tab.
4) Make sure Use Pattern's Pad Properties is deselected.
5) Enter the desired values for Width and Height.
6) Select OK.

Be aware that DipTrace truncates the fourth decimal place (mm) and rounds-off the 3rd decimal place. In the example below, the number representing Pad Y (1.562mm) should actually be 1.5625mm. The dimension 3.12mm on the left side should actually be 3.125mm. The dimension 4.62mm on the bottom should actually be 4.625mm. This is one of many old DipTrace annoyances that can become a trap, and this issue has been pointed out to their staff more than once...


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Last edited by Tomg on 08 Oct 2016, 20:21, edited 1 time in total.

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 Post subject: Re: Help a little shy
PostPosted: 10 Jan 2016, 23:08 
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Joined: 18 Dec 2015, 15:35
Posts: 162
Thanks for the tip on pad sizing and sorry for the confusion over whom I was speaking to.
One thing I noticed is your pattern matches the mechanical part and I've done that more than a few times.

Image

I added .375+.1*2-5.2 to get 4.25 for the inner and .475+.1*2-3.8 to get 2.65 inner
I created a box 4.25X2.65 and placed one pad on the horizontal and one on the vertical axis and then with linear copy and copy mirror finished in about 20 seconds. Exported the drawing with three digit precision to a DXF and imported it. Diptrace handles DXF without issues and I can use my CAD system to draw silk-screens with angled corners.
I found the LGA land patterns information at DigiKey, they recommended .2 toe and .05 sides and heel while another said sides and heel the same size as the pad, I used the same size as it was less work....


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