Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hi Keith,

 

It really depends on the number of boards you want.

If it’s only a couple, a small assembler just needs to know where you got the components, and they’ll hand assemble everything.

On the other hand if you want to do, say, 50-1,000, it may be worth using a bigger company with automated systems.

 

In my experience the larger PCB assembly companies keep stocks of their favourite “preferred” components and can supply you with a list.

This is useful for getting quick prototypes and small runs made as you don’t need to buy large reels of components to suit their machines, and they don’t need to spend time putting loose components onto reels to suit their machines.  Their components may also be a lot cheaper as they buy in much larger quantities.

 

In some cases I’ve purchased and supplied the components myself.  It can be faster than waiting for the assembler to go through their internal process of purchasing, etc, especially if I already have them on hand or they are specialised parts from companies they don’t normally deal with.

Beware though, as some PCB assemblers insist on having components delivered in the manufacturers original packaging (so components are dry and leads are not tarnished or bent, etc).  And rightly so – it’s the only way to maintain high quality control.

 

Sometimes the assembler provides a sourcing service where you can specify exactly what components you want, and they will buy them in, or they will recommend alternatives.  However you will probably end up paying for more components than you need.  This is because the assembler may prefer to buy whole reels of components whereas you would buy exactly the number you need.  They will also buy extra components with the expectation that some will get lost or damaged during the manufacturing process.  Sometimes the assembler will have to buy in a special component for you in much greater quantities than you need (maybe it’s only available in a large MOQ).  If they are really nice, they may store the excess components and offer to sell them to other clients, so you only pay for leftovers if they don’t get used after a few years.

 

Some assemblers just take you design and replicate it, for better or worse.

The best thing is to supply them with as much information as possible, along with a sample board so they can look at it in detail (but be wary of overseas companies that copy your design and sell it on the open market without you knowing – maybe you don’t want to give them firmware or programming details unless you trust them!).

A good assembly house will help you refine your design for production.  If your PCB has surface mount components then they will probably get you to change the component pad sizes to best suit their soldering processes.  Ask for their design rules early in your PCB layout designing.  It may cost more in the short term but end up cheaper in the long run and maybe have a better more reliable product.

 

Good luck,

 

Mark

 

 

I've made a circuit board for myself which does something for my cnc plasma cutting table. There seems to be some sparks of interest for it but not at the cost at which I'd "knock one together" for them. I'd therefore have to look at getting them made in quantity at a professional circuit board manufacturer, but have no idea how they work.

 

Example, when I design a board for myself, I look at what components are available at the right price, then I design my board to suit. 

 

I'm a bit confused though about how the PCB manufacturer chooses the components. They might not have that brand available, or the package is a slightly different size, etc. The board is the easy bit but I don't know how it works with component choice. How do you specify components when you don't know what the manufacturer has available to them, what brand, what quality, etc.

 

Am I making sense.

 

Keith.

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