can someone explain "tooling rail" for smt boards?

[lcipher3]

Not too much smt experience - working on a driver board for some RD.

First Question
I have a 80 pin BGA array package that I *have* to use, with all other thru hole components.
Somebody mentioned I need a "tooling rail". ? Cant figure out what that means.
Is that just a boarder around the board to hold it or??

Second Question - Do you normally order a "stencil" for making the solder paste easier to apply?

 

[vigilante398]

Check this out for a description of the rail: https://www.pcbcart.com/article/content/introduction-on-technical-rail.html

If you're assembling the board yourself, you don't need rails. If the board house is assembling the board, they will usually take care of the rail themselves. I have never manually added tooling for my board designs, even on boards that are getting assembled by the shop.

ABSOLUTELY get a stencil. They're an extra few bucks ($7 where I order) and they add a couple bucks to shipping due to size and weight, but absolutely worth it when you're assembling SMD boards yourself.

Make sure your paste has small enough balls (I always had good results with Chipquick, but I also never did BGAs at home) and get a nice putty knife with a flexible blade for applying paste over the stencil, and you should be good to go.

 

[fig]

ABSOLUTELY get a stencil. They're an extra few bucks ($7 where I order)

Would you share the source? I've wanted to try a stencil over "dabbing" but didn't want to blind-buy one.

TIA

 

[vigilante398]

Would you share the source? I've wanted to try a stencil over "dabbing" but didn't want to blind-buy one.

TIA

I've been using https://jlcpcb.com/ for years, zero complaints with them. You can order a stencil separately from a single gerber file, or you can check a box when ordering PCBs to get a stencil added on from those gerbers. It's cheaper to get it without the frame, but I recommend the frame as it makes it a lot easier to use. Plus the stencils are super thin, so frameless stencils are basically just big razorblades, I've spilled some blood on stencils a couple times

You can save a few bucks on stencils if you combine multiple small designs on one stencil, you just need to put all the board designs into one file and export one big combined paste gerber file.

 

[lcipher3]

Thanks - so its basically making the board a bit "bigger" non-functional perimeter for the handling. - yes?
They always seem to show it (in the examples) as panelized, I guess thats to make things cheaper but not really anything to do with the "rail" requirements.

 

[vigilante398]

Thanks - so its basically making the board a bit "bigger" non-functional perimeter for the handling. - yes?
They always seem to show it (in the examples) as panelized, I guess thats to make things cheaper but not really anything to do with the "rail" requirements.

Yup, it's to make it easier to manufacture. It's something the manufacturer will do when they're building your boards. That's why there are minimum requirements of how many boards you order, they need to have a "panel" of boards that will have a rail around them so they can be big enough to fit in the machines. If a board house was trying to go straight at manufacturing a single 2"x2" board it would get lost in the giant machinery. They have CAD engineers that take your layout and duplicate it the selected number of times to make a "panel" of your design and add rails around it, then your boards are manufactured as a single panel, and after they're completed they are "de-panelized" into the individual boards and the rails and extra material is discarded.

HOWEVER if you have a small design that's less than the maximum size for a standard order (for JLCPCB it's 100mm x 100mm) then you can panelize it yourself to make it cheaper. Like if your board is 50mm x 50mm you could fit 4 of them in a panel, which would save you money if you're getting a large quantity if you panelize it yourself before you upload the file.

But back to the rails, even if you panelize the file yourself you still don't need to add the rails, that will be taken care of on the manufacturer's end, you will never need to worry about that (unless you work for a PCB fabrication plant, in which case they will teach you how to do it )

 

[vigilante398]

Oh I just remembered I have an example I can show you if I remember to get a picture when I get home in like an hour. I work a lot with tubes so I designed a circular board that the tube sockets mount to, and I get them in a panel of 16, but because I order them as a panel and not as individual boards they don't depanelize them before shipping, so I have some that still have rails on them.

 

[Robert]

Some manufacturers have a minimum panel size of around 70x70mm if you want v-scoring. There are a few designs where I've had to add edge rails to meet the size requirement.

Sometimes they'll accept the Gerber as-is and add the rails, other times they'll reject the Gerber and have me add them myself.

Except for exceptionally small boards (like 3PDT breakout boards, SOT23 adapters, etc) I've moved away from panelized boards because I don't like the rough edges left behind after depanelizing them.

It's much more economical if you're ordering a batch or two of PCBs, but my hands are tired of the fiberglass splinters from breaking apart several hundred boards in an afternoon.

 

[vigilante398]

Some manufacturers have a minimum panel size of around 70x70mm if you want v-scoring. There are a few designs where I've had to add edge rails to meet the size requirement.

Sometimes they'll accept the Gerber as-is and add the rails, other times they'll reject the Gerber and have me add them myself.

Except for exceptionally small boards (like 3PDT breakout boards, SOT23 adapters, etc) I've moved away from panelized boards because I don't like the rough edges left behind after depanelizing them.

It's much more economical if you're ordering a batch or two of PCBs, but my hands are tired of the fiberglass splinters from breaking apart several hundred boards in an afternoon.

Oh interesting, I've never had to add rails before. But to be fair all the v-scored boards I've had were rectangular and easy to deal with. This is the only way they'll let me order these:


The gerber file is just the circular board, and they add the mousbites and the rail for me. The very first time I ordered them someone apparently played with flattening the edges of the boards and did a v-score, but I haven't been able to convince them to do that again. This is fine though.

 

[lcipher3]

Oh I just remembered I have an example I can show you if I remember to get a picture when I get home in like an hour. I work a lot with tubes so I designed a circular board that the tube sockets mount to, and I get them in a panel of 16, but because I order them as a panel and not as individual boards they don't depanelize them before shipping, so I have some that still have rails on them.

thanks - makes a lot of sense now

We have a research project that has a BGA component and we were asking a local house to just solder the device for us - and he mentioned the rails. Had we just asked him initially to do the boards AND mount the device he would have just added the rails himself.
Now it makes sense - so we're just going to that house for the whole project. Will be a lot more $ than getting boards from jlpcb but its a rush job.

 

[lcipher3]

Oh interesting, I've never had to add rails before. But to be fair all the v-scored boards I've had were rectangular and easy to deal with. This is the only way they'll let me order these:

View attachment 21757
The gerber file is just the circular board, and they add the mousbites and the rail for me. The very first time I ordered them someone apparently played with flattening the edges of the boards and did a v-score, but I haven't been able to convince them to do that again. This is fine though.

Slick - 9 pin small signal tube? Microphone or pedal preamp or ??

 

[vigilante398]

Slick - 9 pin small signal tube? Microphone or pedal preamp or ??

Yup, mostly 12AX7. Preamp pedals are kind of my bread and butter.