| ??? 10/28/09 22:30 Read: times |
#170157 - My view Responding to: ???'s previous message |
Sorry, but your adapter design doesn't seem to be online anymore, or I'm not supposted to find it by just selecting 'User Pages' and then the link with your name after.
Richard Erlacher said:
I don't see any need for such pads on every signal, but ... if one needed a pullup ... well, there's an opportunity ... and if one needed a rate-limiting cap ... Well, you see what I mean. The problem is board space. There isn't a need for such pads on every signal, if designing a board for a specific chip. But when making a general-purpose adapter/prototype board, you will not know which signals will be in need of pull-up/down or of bypass capacitors. Richard said:
One problem that jumps right out at me, though, is that there are then about 10 cm of trace length between the bypass members and the IC pin, unless one drills holes to shorten the tracks. A solid Vcc and GND plane, as you mentioned, Per, would mitigate this problem. The solution would not work unless every chip signal from the top side has a via to a pad on the bottom side, to minimize the track length to the optional bypass capacitor. It might actually be good to have two via/signal to minimize resistances. Richard said:
Now, for my purposes, the goal would be to make the IC wire-wrap-board compatible. I'm interested in the SchmartBoards since they may potentially speed up the soldering of the chips. But I would want the majority of signals to end up on a different prototype board where the bulk of components are. Maybe a more general-purpose prototype board with space for either the smaller SMD IC and discrete components or for DIL + hole-mounted discrete components. A large number of signals on chips I use either has a component (or short) to GND or to VCC or a component in series with the signals before they are connected to a connector or another chip. So the optimum for me would be an adapter optimized for fast soldering of the TQFP(SchmartBoard?) while supporting low-impedance bypass and easy pull-up/pull-down/series components in 0603 format. If playing a lot with the same chip, I would probably use EagleCad and design a custom dual-layer board with minimalistic support for the specific chip - probably bypass capacitors, crystal with load capacitors, and one or more of SPI/RS232/JTAG interfaces for programming and optionally debug the chip. Then pin headers to connect with a generic prototype board for the rest of the design. I'm now talking playing with as in hobby projects. For prototyping commercial projects, I would most probably start with a dev-kit and then add peripherial logic on a prototype board until I am happy enough that it will be time for a rev-0 PCB. |
