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TSOP-to-SOIC breakout 
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Joined: Sat 01 Dec 2012, 01:50:23

Posts: 240
Location: Oregon, USA
Post TSOP-to-SOIC breakout
So, byuu asked me to help build a reprogrammable Cx4 cartridge out of a MegaMan X2/X3 cart, but that leaves me with the issue of trying to connect a TSOP FlashROM to the wide SOIC MaskROM footprint. The M29F160 that I'm using is nearly as wide as the SOIC. Ideally, I'd love to do castellated edges, but none of the PCB fab houses I normally use will do them. Yes, I could build a breakout with pads and hook it up with wire, but I'm in the mood for something a bit crazy, so having just successfully reflow soldered my first QFN chip, I thought "why not just make the breakout board like a giant QFN chip?" So, I just mirrored the SOIC footprint to the bottom of the board and put the TSOP on top of the board, and here's the result.

Image

0.05" pitch should reflow pretty nicely, without too much chance of shorts. Fun times...

Thu 30 May 2013, 07:25:37
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Joined: Tue 02 Nov 2010, 01:00:37

Posts: 181
Post Re: TSOP-to-SOIC breakout
Hi, nice idea there. Is the board exactly the same width as the SOIC or a bit shorter? In the absence of castellated edges, making it a bit shorter might still help.

A few other suggestions I have:

  • Aren't you going for at least a little neck-down on those pads?
  • Plane connect style to pads seems to be somewhat arbitrary, too. You should usually go for a thermal relief connect style or some pins might not reflow/solder on correctly.
  • Power tracks are somewhat wide. The thing doesn't eat a lot of current to begin with, so you don't need to make the reflow/solder job that much harder by using 0.5mm tracks (or whatever that is).
  • Push/stagger the 6 vias on the left so the plane can get through them.
  • Take the track that goes from btm right to top left across the board (below the 6 vias; A16?) towards the inside of the PCB some more so an additional via can fit there to connect to the bottom plane.
  • There is an awful lot of pins NC on the left side of the TSOP. I'm guessing pinout is somewhat like S29GL032N. So you effectively left high address lines floating. So if you ever come across cheap 64M chips, you wouldn't be able to use them as direct replacement. At least tie them directly to ground or make additional solder pads on top like you did for WE#, but have a little cuttable track connect them to ground.
  • Bridge between 48 (BYTE#?) and 47 (VSS?) seems unnecessary when you connect both to the plane anyway.
  • Pin 12 (RESET#?) should probably be tied to VCC instead of left floating.

cYa,

Tauwasser

Thu 30 May 2013, 12:47:00
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Joined: Sat 01 Dec 2012, 01:50:23

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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
  • The board is slightly narrower (by about 1mm) than the SOIC footprint, so the SOIC pads will show under the board, to help check for alignment and, if necessary, help clean up shorts (reflow shorts tend to show up on the edge of a chip, not under it, so I'm hoping the same here)
  • I'm not sure what you mean by neck-down
  • The plane connect to the pads is just how EAGLE does it, I don't think I can change that
  • I'm just used to making large power tracks, my PCB design work is all self-taught, and I've never learned thermal design (or high-speed design... I really need to, but so far I've never done a high-speed board)
  • The NC pins on the top of the TSOP (relative to the photo's orientation) are a pin called RP# (not explained in the datasheet), R/B# (a busy indicator), and three internally N/C pins. The ones on the bottom that are NC every other pin are A8-A14, which are not used because it's in 8-bit mode.
  • The bridge between 48 (BYTE#) and 47 (VSS), again is how EAGLE does plane fills
  • The datasheet calls pin 12 RP#, and the only indication of its function is in the block-protect override sequence. I suppose it wouldn't hurt to connect it to Vcc, but I'm not sure that it actually is a reset signal

Here, I connected pin 12 to Vcc and improved the ground plane a bit:
Image

Thu 30 May 2013, 18:22:20
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Joined: Tue 02 Nov 2010, 01:00:37

Posts: 181
Post Re: TSOP-to-SOIC breakout
qwertymodo wrote:
I'm not sure what you mean by neck-down


Neck down is the ratio of the pad width to track width. Yours would be 1, since the tracks are as wide as the pads. Usually, you would design the tracks somewhat smaller than the pads. Altium Docu.

qwertymodo wrote:
The plane connect to the pads is just how EAGLE does it, I don't think I can change that


That seems unfortunate. Quick googling seems to cornfim this :-/

qwertymodo wrote:
I've never learned thermal design


I'm used to Altium. There, it's just an option in the Design Rules. Basically, you connect the plane using small tracks and keep some distance from the actual polygon. For a round pad, you would usually see 2 or 4 tracks connect to the plane, not the pad completely inside the plane. It kind of looks like spokes of a cart wheel. Altium Docu.

qwertymodo wrote:
The NC pins on the top of the TSOP (relative to the photo's orientation) are two pins called RP# (not explained in the datasheet), R/B# (a busy indicator), and two internally N/C pins. The ones on the bottom that are NC every other pin are A8-A14, which are not used because it's in 8-bit mode. [...]
The datasheet calls pin 12 RP#, and the only indication of its function is in the block-protect override sequence. I suppose it wouldn't hurt to connect it to Vcc, but I'm not sure that it actually is a reset signal


Well, the internal NC pins are the ones that higher volume devices use for additional address pins. So I still suggest connecting those to ground. As for RP#, I assume you intend to use a Micron 29Fxxx device. The datasheet I found indeed does not state explicitly what the use of it is. However, the 28Fxxx datasheet does:

Quote:
RP# Input Reset/Power-Down: When LOW, RP# clears the status register, sets
the ISM to the array read mode, and places the device in deep
power-down mode. All inputs, including CEx, are “Don’t Care,”
and all outputs are High-Z. RP# must be held at VIH during all
other modes of operation.


So my suggestion of connecting it to VCC still stands :) This would also match the pin-out of other devices, so I assume functionality is somewhat the same anyway.

cYa,

Tauwasser

Thu 30 May 2013, 18:43:42
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Joined: Sat 01 Dec 2012, 01:50:23

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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
Yes, I'm using a Micron 29F160. As for the neck-down, I can't go any smaller with my traces without hitting the fab minimum (absolute minimum is 6 mil, recommended >8 mil, I'm using 8 mil). I'm not too worried about the thermal characteristics of the TSOP footprint, since I'll be hand-soldering that. I'll only be reflowing the two boards together. What you describe about planes connecting to pads with a small trace on 4 sides is exactly what EAGLE does, and that's likely what it is trying to do when it connects adjacent pads together (because it's connecting the left side of one to the right side of the other with a small trace). Also, as I said, I did end up connecting RP# to Vcc, so no problems there. As for the higher address pins, are there any higher-density parts available in 5v? If not, then there's no point, because I'd need a whole new board anyway.

Thu 30 May 2013, 19:01:44
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Joined: Tue 02 Nov 2010, 01:00:37

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Post Re: TSOP-to-SOIC breakout
Well, usually the connect style only applied to direct connections, not pad to pad when pads are in plane - at least in Altium. So it seems Eagle's plane connect lines are the same (minimal) width you specified for all traces, which is why the connections look so bulky. I guess you can't do anything about that then.
Although I have successfully used .15mm tracks in fab houses that wanted 6mil minimum, so it's definitely possible to be outside the safe range and still have it fabbed alright - though most Chinese fab houses seem to state they can do 6mil, but only 8mil will be reliable. Actually, a blog post from either Seeed or iTead (can't remember which; I have used both recently) goes so far as to state that they seek minimum prices for customers when ordering 10 boards (supposedly all 100% e-tested), so they figure there are at least 3 to 4 good, usable ones... When I as a silly customer would expect all 10 100% e-tested PCBs to work, silly me :D

cYa,

Tauwasser

Thu 30 May 2013, 19:10:58
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Joined: Sat 01 Dec 2012, 01:50:23

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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
I went ahead and connected A21 and A22 (A20/21 on the chip) according to the M29EW pinout, which varies slightly from the M28F pinouts (i.e. pin 15). As for the width of the plane connection trace, that is actually configurable, but I had it set to 8 mil as well, hence the fact that it was the same width as the other traces. Well, ok, I just realized that the Vcc pads in the upper right and the Gnd pads in the upper left (of the bottom SOIC footprint) I did actually connect myself, those aren't ground fill connections.

Image

Thu 30 May 2013, 19:34:58
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Post Re: TSOP-to-SOIC breakout
qwertymodo wrote:
I went ahead and connected A21 and A22 (A20/21 on the chip) according to the M29EW pinout, which varies slightly from the M28F pinouts (i.e. pin 15).


But the M29EW is a TSOP-56, while the M29F is a TSOP-48... Do you intend to leave the upper-most four address lines dangling? Also, the M29EW is a 3.3V chip, so it seems a poor choice for the SNES.

cYa,

Tauwasser

Thu 30 May 2013, 20:48:44
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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
There's a 48-pin TSOP version too. I don't actually intend on using the M29EW, Micron just doesn't make an M29F in 32/64Mbit, so I couldn't find the right pinout, so I just picked another part family that had the same pinout so I could figure out which of the NC pins on the M29F160 should go to A21/A22. For my purposes, I don't actually intend on using anything larger than 16Mbit, I just figured I might as well hook up those pins...

Edit: Actually, I guess it's the M29W, not the M29EW that comes in 48-pin. My bad...


qwertymodo


Thu 30 May 2013, 21:46:22
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Post Re: TSOP-to-SOIC breakout
Oh, now I gotcha. Well, the safest bet would then to go with a JEDEC 21-C pinout, particularly JEDEC 21-C 3.5.2.6, see Word Wide EEPROM (registration free but mandatory).

EDIT: M29W is still 3.3V, just so you know.

cYa,

Tauwasser

Thu 30 May 2013, 21:52:29
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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
Yeah, the M29F/M29W match the JEDEC pinout, except the JEDEC pinout doesn't indicate where A22 (well, technically A21...) should go on a 64Mbit chip in the same package, so I'm going with the Micron assignment of pin 13.

Thu 30 May 2013, 22:00:49
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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
Ok, I got PCB's in today. In retrospect, I wish the board was just a little bit wider, it made mounting a bit tedious, making sure that I made proper contact on both sides. I'll need to spend a bit more time with the hot-air rework station, since there are a few disconnects and a few shorts, but if I can get all of those worked out, it's looking pretty slick. I haven't soldered on the actual chip yet, because I'm waiting for a TSOP socket so I can burn a ROM to it before I solder it on. Eventually, the idea is to be able to write to the ROM via the cart slot, but I'd like to have a ROM on the chip before I solder it on so I can at least run a quick power-on test once it's all assembled. So byuu, I'm still working on it, but it's getting there :D

Image

Fri 28 Jun 2013, 23:02:34
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Joined: Sat 01 Dec 2012, 01:50:23

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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
Dangit, I just ripped up about 6 pads trying to rework it. This board's toast :( I guess I should pick up some cheap SFX boards to test on, so I don't ruin another copy of a $30 game (maybe Star Fox, but then I run the chance of getting an epoxy board). I can pick up Stunt Race FX on Ebay for $6, guess that'll work. If I succeed, I can always turn it into a Star Fox 2 repro...

Sat 29 Jun 2013, 00:11:49
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Joined: Tue 02 Nov 2010, 01:00:37

Posts: 181
Post Re: TSOP-to-SOIC breakout
Don't trash it! Just scrape some of the solder stop off of the respective tracks and use verowire to make the connection to the side...

cYa,

Tauwasser

Sat 29 Jun 2013, 00:41:22
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Location: Oregon, USA
Post Re: TSOP-to-SOIC breakout
Yeah, I'll give it a shot... I was really hoping to avoid dead-bug wiring, but considering the cost of the board, it's probably worth it to at least try.

Sat 29 Jun 2013, 01:10:49
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