Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Butt-joints

Mark S

#3034

Butt-joints | 13 September, 2000

Hi All -- I have read the IPC acceptability requirements of butt-joints, but haven't seen anything on how they're actually performed. I'm assuming we can trim a DIP package, and place the part onto paste immediately before relow (or hand-solder it later in the process). Has anyone had experience (successful or otherwise) with butt-joins?

For what body-to-PCB clearance should the parts be trimmed?

Do we need to 'tin' the ends of the DIP leads after they are trimmed to avoid oxidsation of the exposed base conductor material? Given that the 'butt' of the lead is but a small fraction of the wettable surface area, what effects would there be of a non-wetted butt within the solder join?

Thanks to all -- I'll look forward to your advice.

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#3035

Re: Butt-joints | 13 September, 2000

Why not form them as gull wings? Butt joints are undesireable for the very reasons you mention.

Further, why the hey are you doing this? By the time you get done putzing around with this, you won't save dip. Just go out and sell those crappy DIP and then buy the correct parts.

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Mark S

#3036

Re: Butt-joints | 14 September, 2000

.... an 18-20 week lead-time is why we're doing this. Ideally I'd prefer to form them into gull-wing (except we'd have to do it by hand and that'd be difficult to control), but it's a hell of a lot quicker and more consistent just to run them through the DIP-prep trimmer. Thanks for your advice.

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#3037

Re: Butt-joints | 14 September, 2000

Have a project that use to have them. End up getting a little grayer every time they came around. Finally got the design Engineer to redesign the board with through holes. Now the part is used the way it was intended to be! Ended up costing us more money to get them prepped as a butt joint lead and had longer lead times. Everyone loved the idea of changing it to a through hole, well except my counterpart in the leaded area. But, he needed a few more problems :^)

Get it redesigned so you can use it as a DIP component!

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Brian W.

#3038

Re: Butt-joints | 14 September, 2000

It really isn't that difficult to control. Have one of your mechanical or manufacturing engineers design a quick little fixture. We used to have the same problem, then we designed a two piece fixture out of aluminum. We also had our own tape and reel, so we would tape them after forming. Saved many, many problems.

Brian W.

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Boca

#3039

Re: Butt-joints | 14 September, 2000

Of course the others have great answers, try NOT to do it, for all of their reasons.

However, had to do it in the past, OEM, custom chip, die wouldn't fit in a SM package, volume wouldn't support a second package type ...... and on and on.

So we used a Dip trimmer machine, had to make a couple of parts to help the machine trim closer to the body, height is something you set per your product requirements, our biggest concern was coplannarity. You have to get the machine to consistantly cut the leads coplannar to within a few mils because the solder paste printed on the fab is only 6 or 7 mils thick and all of the leads have to reach the paste.

Reliability in the OEM's product was pretty good, they have lots of lead so they have a lot of compliance thru thermal cycling.

We even build products today, contract shop, that use the butt cut IC's. Not fun, but if its gotta go....

Boca

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