ProtoTyping PCB Techniques 1

[europus2002]

Hi All,
Want an input from all you guys.. What is the most preferred way of getting the 1st prototype PCB..... I have few ways i do it...But would appreciate inputs from all you people...
1) Start building the design on General purpose PCB
and go on trimming your design for precision..
2) Throw the whole schematic to PCB fabricators/
assemblers
3) Get the boards made and polpulate the components
your self...
I am following the 1st one where i use throughhole components and later change the board layout to SMD..

Is anybody recently started with Bread toaster reflow method??? Wondering if it's simple to pickup or need some experience....thanks in advance..

 

[VEBill]

For most situations, 'preferred' means fastest.

Fastest is probably to order a small qty of PCBs from a fast-turn-around PCB house and then populate them yourself (assumes that you have the required parts on hand).

For the inevitable design changes, just repeat the cycle. Plan for a couple of times around the loop.

One could imagine that each design cycle might be as quick as only a couple of weeks if everything goes well. That's better (faster) than most other options.

 

[VEBill]

PS: If you can efficiently communicate this to your PCB house, it can be useful to allow flexibility on the PCB. In other words, make the layout a bit more flexible by providing spare pads, pads for alternate packages, room for cuts and jumpers.

Every time that we've left such flexibility on the PCB, we've used it.

 

[itsmoked]

europus2002;

The way I do it is to make a reasonable (quick) stab at the final design. This has the great advantage of educating you to your designs physical gotchas. Things like where you thought the mounting holes shouldve been and where the connectors are. Then after hand stuffing the board/s (learning about any assembly gotchas) you just hack the dickens out of this board. To add any fixes or make changes you can glue added parts on and jumper to them (not a problem). This all provides you with a solid running foundation for continuing development.

I use the toaster oven method regularly. It works quit well. Make sure you get an oven that will get hot enough and will afford you a reasonable view of a board being processed. I can give you a model number if you desire.

I have done the 'solder paste in a syringe' method, the stencil method, and the hand solder method. I would probably not bother with the solder in a syringe method unless there were special circumstances, this after using it a few times.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[europus2002]

Thanks VE1BLL & itsmoked...I appreciate your inputs. I was curious about the methodology you all were following which is different than mine. I have been using the GPB hand solder method for last 6-7 years but thought of doing it differently this time and got the PCB made and populated the components & VOILA !!! It all worked....I have more questions for itsmoked...
1) what is the "solder in syringe" method??
2) when will you prefer using it ?
3) How do you cut stencils?
4) Where do you order your solder paste from? Any perticular brand & grade?
5) Can't you directly rub solder paste one the whole board , stick components and toast it??
Can you describe your method in brief? Any websites?
what do you do about the connectors and box headers?
)....thanks in advance

 

[itsmoked]

You're welcome europus2002.
SEE ###

1) what is the "solder in syringe" method??
### You can buy solder paste in a syringe. I get it often from DIGIKEY. It isn't cheap! About $50 because they require you ship it *overnight* only because it changes with heat like sitting in the back of a truck. Once I receive it I either use it immediately or throw it in my refrigerator. Everyone knows not to spread it on toast. Actually we use the otherwise worthless butter hatch in the refrigerator. You must remove it about two hours prior to use. Everyone sez it's worthless after a day or two but I have used it up to a year later.

You just take the syringe and blob a little on each and every pad on the board to be soldered(this is strictly surface mount I'm talking about). Then you just place the parts. It is pretty forgiving. This breaks your task into dabbing the whole board then placing the parts as opposed to soldering one pad of every part then using tweezers tacking one pin of every part to the soldered pads then soldering all the other pins all at the end.

Let me say here; it is not necessarily better to use the dab with a syringe method.

2) when will you prefer using it ?
### I have done it about 20 times.. I have concluded that it doesn't seem to save much time over an orderly hand soldering scheme. Plus it has the added urgency heaped on it because you can't leave the paste sit all night like you can walk away from a hand solder job.

3) How do you cut stencils?
### No stencils in the syringe method discussed.
If I am going to make more than five boards(of course this depends on the boards) I then go to "Stencils Unlimited" on the web and they whack out a stencil quickly and send it to you.(about $100) Make sure you get their little kit, (I think it's free), that has a sqweegee and guides and such. That works very well.
I have done small production this way.. (hundred pieces) Five or ten at a time as your neck allows.


Let me warn you [purple]IT IS NOT POSSIBLE TO HAND STENCIL ANY PARTS WITH LESS THAN 25MIL LEAD PITCH[/purple] Trust me, I have tried it over 400 times and have never once succeeded. The process needs far, FAR, more rigid control than is available to a shop without temp control and mechanical systems.

4) Where do you order your solder paste from? Any particular brand & grade?
### Sadly

http://www.stencilsunlimited.com/

doesn't carry any aqua solders so I have to look elsewhere. U can get it from DIGIKEY in jar or syringe or any purveyor of soldering supplies. I have gotten it from

http://www.wassco.com/

. Because the sub 25mil stuff needs uncompromising uniform, specific consistency it is usually a bit of a hassle because you have things like calls patched through to salesmen who keep it in refrigerated caches and rush it to shipping or to you directly.
As I said I use aqua solders so I can clean them with hot water. If you are happy using extra chemicals like people who make their own boards (sheesh) then you can get solder from S.U.

5) Can't you directly rub solder paste on the whole board , stick components and toast it??
### No. You have to apply it as carefully as possible.

Can you describe your method in brief?
### Paste as described above.
### Preheat oven as hot as it goes.. 450F ish.
### Using tweezers place a single board into the hot oven.
### Watch for melting solder. It will melt from the inner(oven) side to the outside(door/window). The solder will go from grey to silver like a wave across the board. Once the last area has switched to silvery wait about 5 seconds more and remove the board with tweezers and set it on a metal surface. If you have parts with large under part areas like caps wait about 10 seconds after last silver appears. Do not delay as the board will be quickly charred, causing much hideous stink that will plague you for about 3 days. Plus the board is destroyed.

Any websites?
### As mentioned.

What do you do about the connectors and box headers?
### If they are SMD.. Nothing. Treat them like any other SMD part on the board. If they are thru-hole, solder them by hand later.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

I'm with Keith on the "Make the PCB immediately and hack the crap out of it, as needed, later" deal. I would say 50% of my boards get a respin from the prototype due to component size tolerance mismatches and or component inclusion/exclusion, but I've never respun a board more than once. The other 50% of the time that proto board simply moves directly into production, saving a lot of time (time that was spent up front making the proto board a quality layout).

I typically hand solder everything, but I've been itching to pick up a toaster oven and put a little PID controller on it, turn it into a miniature reflow oven with programmable temp profiles and all. Someday...


Dan
Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

Hi Ho Dan.

Skip el PID. I set up a cheap-o Cal panel PID with a hockey puck on an enormous chunk of heat sink. It's plumbed with a male female set of plugs so I can plug the whole thing into the wall then plug whatever into it. e.g. the toaster oven. It worked fine but often fought with the oven safety (which the lawyers have designed into all the ovens these days).

Well I had a fellow EE by to show him the process and of course the Cal promptly failed as I turned it on for him. So we just unplugged the oven and stuck it into the wall and ran it on max. Since you have to observe the boards the temperature is only marginally important. +/- a fifty degrees around 425F will work fine. Because the oven element kicks on and off occasionally and directly radiates the board you have to watch the boards closely.

You will find though on a board run that if the first board solders in 2 minutes and 16 seconds all the rest will be within a few seconds of that time.

Profiles be damned! lolo

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com