How to add 0R 1206 Resistor as Jumper t o Board Layout

On 7/3/2010 12:44 PM, uMinded wrote:

I have seen 0R SMT jumpers used on a few prototypes and they where used

for this reason:

The company has in house board manufacturing but only for 2-4layers and

during development the board was too complex for a 4layer routing and

they used SMT jumpers that looked like resistors but where just wire

bridges in a standard SMT package. They where not on the schematic as

the guy who routed the board just added them to get those last few

airwires routed. This worked but if I saw a commercial product with that

I would stay away as they where obviously cutting corners or cheap.

>

They are "obviously" cutting corners? I thought 2 layer boards are much

more reliable than 4 layer boards. What is wrong with wanting to save

their customers' money, is that being "cheap"? Once again, no logical

objective reason that I can see...

If an SMT resistor is reliable, why would an SMT jumper be less

reliable? If you could somehow tell that there were a few extra

resistors on a board, would you declare it to be cheap or cutting corners?

I suspect the real reason this is not done more often is simply that CAD

tools don't handle it gracefully. But if someone does have an answer to

why it is a bad idea, I'd like to hear it...

The second reason to use 0R jumpers is the acceptable reason. If you

What makes them "acceptable" in this context but not in a jumper layer

context?

By the way, the disk drive in question was from the top rated

manufacturer and was produced in the early 2000's. In my experience,

volume commodity manufacturers favor double or single (yes!) layer

boards wherever possible.

On 2010-06-12 00:22:30 +0200, Gary Gofstein <nospam@use.forum.net> said:

If it sounds like I'm preaching, I'm not; but I have asked this

question many times and I have never gotten a satisfactory answer. Is

there something wrong with using a jumper layer that I don't know

about? Or is it just that it is too time consuming or impossible to

make one on most EDA tools?

There are several ways to handle jumpers, I use two of them. I etch the

first edition of most boards myself.

1) I route long jumpers on the top layer and use bare wires. Make the

tracks going to the via as fat as possible, preferably the same

diameter as the via, so the eyelet will stay on the board when you

drill.

2) short jumpers are done with 0R reistors, 1206 foorprint. Yes, these

need to be in the BOM, so also in the schematic. See attach. Yes, I

ignore the airwaire on the board.  These 1206 jumpers are used mostly

for connecting GND planes, i.e. different parts of the same polygon.

Soldering an 1206 0R resistor is a lot less work than drilling two

holes and wiggling a wire through them. For boardhouse made boards, 2

layers is enough for me.

Yes, it would be nice if Eagle could see the jumper as part of the net,

but this would involve different treatments of components that are part

of the net and components that are not. A different layer would not

solve that.

--

Eur van Andel  eur@fiwihex.nl

Eur van Andel wrote on Mon, 12 July 2010 08:10

short jumpers are done with 0R reistors, 1206 foorprint. Yes, these

need to be in the BOM, so also in the schematic.

SMD resistors used in this role should not be on the schematic, since they

are a artifact of routing, and do not relate to the circuit itself.

Currently there is no way to do this in Eagle, but that would be a nice

idea.

Quote:

Yes, it would be nice if Eagle could see the jumper as part of the net,

 

but this would involve different treatments of components that are part

 

of the net and components that are not.

I think if this were added it would have to be in the ROUTE command where

it understands special packages you define as jumpers.  You should be able

to place them anywhere in a route, just like vias.  There would need to be

a list of allowable jumpers per net class so that the auto router knows

what it can do.  Each type of jumper would also need its own cost in the

auto router.

Note that these jumpers must not show up in the schematic.  You must be

free to add them or rip them up without having to edit the schematic.  They

do need to be in the board data so that BOM tools can find them.

While all this is nice, it sounds like it would be considerable effort to

add to Eagle.  If I got to pick I'd rather CadSoft work on more flexible

package definition so that you can suppress some DRC errors from deliberate

overlaps within a package, and allow for multiple symbols per device (gate)

with possibly different numbers of pins.

--

Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

On 7/12/2010 5:10 AM, Eur van Andel wrote:

On 2010-06-12 00:22:30 +0200, Gary Gofstein <nospam@use.forum.net> said:

>

>> If it sounds like I'm preaching, I'm not; but I have asked this

>> question many times and I have never gotten a satisfactory answer. Is

>> there something wrong with using a jumper layer that I don't know

>> about? Or is it just that it is too time consuming or impossible to

>> make one on most EDA tools?

>

There are several ways to handle jumpers, I use two of them. I etch the

first edition of most boards myself.

>

>

1) I route long jumpers on the top layer and use bare wires. Make the

tracks going to the via as fat as possible, preferably the same diameter

as the via, so the eyelet will stay on the board when you drill.

>

2) short jumpers are done with 0R reistors, 1206 foorprint. Yes, these

need to be in the BOM, so also in the schematic. See attach. Yes, I

ignore the airwaire on the board. These 1206 jumpers are used mostly for

connecting GND planes, i.e. different parts of the same polygon.

>

Soldering an 1206 0R resistor is a lot less work than drilling two holes

and wiggling a wire through them. For boardhouse made boards, 2 layers

is enough for me.

>

Yes, it would be nice if Eagle could see the jumper as part of the net,

but this would involve different treatments of components that are part

of the net and components that are not. A different layer would not

solve that.

>

>

I have heard that some CAD packages have a designated jumper layer that

they can route on. The rules for this layer are derived from the type of

jumper that are allowed to be generated ( fixed length wire, 0R thru

hole resistor, 0R SMD resistors ). This allows the CAD software to keep

track of the net connections ( through the special layer) and keep these

jumpers off the schematic. It is not just another copper layer, EAGLE

already has plenty of those. The special layer is not ever output, just

used to contain the routes that belong to the jumper components.

There are a lot of ways to make the software handle a "jumper layer"

functionality...I was just pointing this out as an example.

The reason for bringing up the topic in this thread is not related to

how work around the problem in EAGLE, but rather to a poster's assertion

that the jumpers /must/ appear in the schematic. I believe the original

poster was talking about "jumper layer" jumpers rather than "option

selecting" jumpers and that these kind of jumpers are not needed or

desired in the schematic, only the BOM.

On 7/12/2010 6:15 AM, Olin Lathrop wrote:

Eur van Andel wrote on Mon, 12 July 2010 08:10

>> short jumpers are done with 0R reistors, 1206 foorprint. Yes, these

>> need to be in the BOM, so also in the schematic.

>

SMD resistors used in this role should not be on the schematic, since they

are a artifact of routing, and do not relate to the circuit itself.

>

Currently there is no way to do this in Eagle, but that would be a nice

idea.

>

Quote:

>> Yes, it would be nice if Eagle could see the jumper as part of the net,

>>

>> but this would involve different treatments of components that are part

>>

>> of the net and components that are not.

>

I think if this were added it would have to be in the ROUTE command where

it understands special packages you define as jumpers. You should be able

to place them anywhere in a route, just like vias. There would need to be

a list of allowable jumpers per net class so that the auto router knows

what it can do. Each type of jumper would also need its own cost in the

auto router.

>

Note that these jumpers must not show up in the schematic. You must be

free to add them or rip them up without having to edit the schematic. They

do need to be in the board data so that BOM tools can find them.

>

While all this is nice, it sounds like it would be considerable effort to

add to Eagle. If I got to pick I'd rather CadSoft work on more flexible

package definition so that you can suppress some DRC errors from deliberate

overlaps within a package, and allow for multiple symbols per device (gate)

with possibly different numbers of pins.

>

This is also an excellent way to do it. The advantage of the dedicated

layer approach is that it only requires relaxation of some of EAGLE's

rules to implement the functionality, rather than new functionality.

In this way it is analogous to the examples you've given where EAGLE's

insistence on 1:1 correspondance and enforcing rules that are meant to

keep newbies out of trouble are becoming a problem. A warning is more

appropriate than a prohibition in these cases...