creating a memory footprint and schematic
ALL VALUES ARE IN mm UNLESS OTHERWISE STATED
"Woe, oh woe I be certainly."
I've no idea what I'm doing but I found this guide: http://wiki.altium.com/display/ADOH/Creating+Library+Components#CreatingLibraryComponents-CreatingPCBComponentFootprints
FYI we are creating a footprint for AS7C38098A-10TIN. Here is its datasheet
The "400mil" in the component's name references its width, by the way.
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"Leads": the metal thingies that stick out that we are going to solder on to the PCB.
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Source: I just made that up.
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"Lead pitch": The distance between the leads, measured centre-to-centre.
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Source: http://en.wikipedia.org/wiki/List_of_electronics_package_dimensions
Wait, what? What kind of component is a memory chip?
- Ball Grid Arrays (BGA)
- No this is more like, a CPU or microprocessor.
- http://en.wikipedia.org/wiki/Ball_grid_array
- Capacitors
- No
- Diodes
- No
- Dual In-Line Packages (DIP)
- Edge Connectors
- Leadless Chip Carriers (LCC)
- Pin Grid Arrays (PGA)
- Quad Packs (QUAD)
- Resistors
- Nope.
- Small Outline Packages (SOP)
- Yes: on the farnell page it says "Memory Case Style: TSOPII".
- TSOP stands for "Thin Small Outline Package". According to the datasheet the chip is also available as a 48-ball TFBGA, but I'm going to trust Farnell on this one.
- Staggered Ball Grid Arrays (SBGA)
- Staggered Pin Grid Arrays (SPGA)
What dimensions should the pads have?
Whoa, whoa. Pads != leads. Shit, the pads are the holes?
- Width ( Note: Width is the vertical one in the window. )
- Assuming Lead Width is "b".
- b_min = 0.30mm, b_max = 0.45 -- The fuck?
- oh well. (b_min-b_max)/2 = 0.075mm
- Length ( Note: Length is the horizontal one. )
- There doesn't seem to be any direct Lead Length measurement in the datasheet.
- (E_nom-E1_nom)/2 = (11.760mm - 10.160mm)/2 = 0.8mm
- Horizontal one
- uh, (E-E1)/2 + E1?
- == 10.160mm + 0.8mm = 10.96mm
- Vertical one
- ooh this looks like lead pitch
- which is e on
You know what this shit is making no kinds of sense. At all. I am going to postpone this and make the component for use in altium before the footprint.
Also known as "all kinds of better".
NOTE: The following describes the process to create a footprint for the memory chip. Please check out the actual guide on the altium wiki if you are creating a footprint for a different component.
Apparently altium has another footprint wizard that accepts the dimensions of the chip rather than that pad shit we were doing just now.
That shit is super legit.
SOP/TSOP
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Wizard label (letter)
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equals what in the datasheet (page 10)
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Width Range (H)
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E: E_min = 11.506mm, E_max = 12.014mm
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Maximum Height (A)
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A: A_max = 1.20mm
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Maximum Standoff Height (A1)
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A1: A1_max = 0.15mm
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Body width range (E)
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E1: E1_min = 9.957mm, E1_max = 10.363mm
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Body Length range (D)
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D: D_min = 18.212mm, D_max = 18.618mm
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Number of pins = 44
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Lead Width Range (B)
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b: b_min = 0.30mm, b_max = 0.45mm
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Lead Length Range (L)
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L: L_min = 0.40mm, L_max = 0.60mm
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Pitch (e)
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e: e_nom = 0.8mm
There is nothing in the datasheet about thermal pads.
There's no given value in the datasheet, so I'm going to trust altium on this one.
???? Again, trusting Altium here.
I just clicked through it and used the recommended values because the datasheet didn't mention any of it.
Basically I did what that said and looked at the memory chip components created by 256SoG.
See page 2 and 3 in the datasheet.
I copied 256SoG here because I had no idea what these things do. I expect one of them should map to the similarily numbered pin in the footprint (automagically), but I've no idea which one.
So:
- Display Name => Symbol (A0-A18 etc)
- Designator => The number (1-44)
| Pin | Electrical type |
|---|---|
| Vcc | Power |
| Vss | Power |
| A | Input |
| DQ | I/O |
| CE# | Input |
| WE# | Input |
| OE# | Input |
| LB# | Input |
| UB# | Input |
Compiled it as an integrated library and added that to the repo.
- .PcbLib => footprint library (contains the memory chip footprint)
- .SchLib => schematic library (contains the memory chip component schematic)
Add the .schlib file to the project's library and select the component from the Libraries menu. Bam.