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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Through-hole/SM mix

Steve

#17875

Through-hole/SM mix | 12 October, 2001

I need help with a process issue. I am dealing with a board design that is double-sided SM with a couple high density through-hole devices. I want to flow solder the through-hole stuff, so what is the best way to deal with them? Since one of the through-hole devices restricts SM after it is mounted, the flow of the through-hole needs to happen after SM.

Should the SM be soldered using high temp paste? Should the SM components on the solder side be masked during the through-hole flow?

Ideas from people doing similar processes would be greatly appreciated.

Steve

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David Brink

#17876

Through-hole/SM mix | 12 October, 2001

Steve

Often solder mask is the only solution but in many cases there is enought space between smt and thru-hole to utilize a component masking wave solder pallet. The advantage to a pallet is consistancy of results and excellent protection of masked parts. If your PCB allows for this approch it should be considered. I manage design at EMC Global Technology. We design and machine all kinds of fixtures. There are other sources for wave solder pallets that can be found on the web.

David Brink

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Ken Bliss

#17880

Through-hole/SM mix | 13 October, 2001

I agree with EMC based on what you described, and they build good pallets along with a few others, a small word of caution is that pallets are bit expensive typically several hundred dollars or more each. So if you find that is the road you go, be sure to determine a method of storing them safely in a cart or shelf rather than just stacking them in a pile. I mention this because I see this problem everywhere, and a lot of pallets getting damaged. Use a pcb type storage cart from any of the cart companies like metro, carri all, mossman tubbs, etc. and a few companies including http://www.blissindustries.com make one specificly for that purpose. The key is to keep the pallets stored on their edge just like they go down the conveyor and they do not touch each other. The carts that are all metal are the best as you can also store hot pallets right out of wave solder machine.

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#17883

Through-hole/SM mix | 15 October, 2001

Before this wave solder pallet salesman blather gets too far out-of-control, let�s stop for a minute. The three major approaches you have are:

1 SELECTIVE SOLDERING: Using: * Specialty wave soldering machine to solder specific areas of a board * Peculiar wave solder pallet on a standard wave solder machine to allow soldering specific areas, while block other areas from contact with the wave.

2 INTRUSIVE REFLOW: Using: * Paste printed on PTH pads and then reflow soldered. * Component leads where the fabricator has added solder deposits, that are reflow soldered. [This is mostly applied to connector, though.]

3 STANDARD WAVE SOLDERING: Epoxy your secondary side components in place, rather than reflowing solder paste, and wave solder your PTH and your second side SMT at the same time. This probably will require a wave soldering machine that has two solder pots.

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#17884

Through-hole/SM mix | 15 October, 2001

Who are other selective solder pallet suppliers that we should consider?

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#17891

Through-hole/SM mix | 15 October, 2001

Adding to Dave's comments, suppliers of selective soldering machines include Air Vac and Wenesco. I've used both, to solder and de-solder larger thru hole parts, such as connectors and large IC's. They are best suited to lower volume applications, and if needed they can be used to remove those big thru hole parts .

My personal experience was at different jobs, with an Air Vac machine on smaller boards and a large Wenesco machine on a large board where a 100 pin connector mounted from the back on a thick board.

Both are versions of what I call a "flowing solder pot", where a small pump pushes solder up through a chimney. You place the board over the nozzle and hit a switch, the pump comes on for a set time, and your part is soldered. Different nozzles are available, and I'm sure you could get a custom size made.

Another source of selective soldering pallets is Stone Mountail Tool. You can also ask your wave solder machine vendor for a recommendation.

As mentioned, these can get expensive and may not work well on your production line. The pallet has to cool before it can be used again, and will need regular cleaning to remove flux residues.

Good luck, Mike

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#17892

Through-hole/SM mix | 15 October, 2001

Adding to Dave's comments, suppliers of selective soldering machines include Air Vac and Wenesco. I've used both, to solder and de-solder larger thru hole parts, such as connectors and large IC's. They are best suited to lower volume applications, and if needed they can be used to remove those big thru hole parts .

My personal experience was at different jobs, with an Air Vac machine on smaller boards and a large Wenesco machine on a large board where a 100 pin connector mounted from the back on a thick board.

Both are versions of what I call a "flowing solder pot", where a small pump pushes solder up through a chimney. You place the board over the nozzle and hit a switch, the pump comes on for a set time, and your part is soldered. Different nozzles are available, and I'm sure you could get a custom size made.

Another source of selective soldering pallets is Stone Mountail Tool. You can also ask your wave solder machine vendor for a recommendation.

As mentioned, these can get expensive and may not work well on your production line. The pallet has to cool before it can be used again, and will need regular cleaning to remove flux residues.

Good luck, Mike

reply »

#17907

Through-hole/SM mix | 16 October, 2001

Adding to Mike's comments. There are two types of selective wave soldering machines. * Chimney type, like the AirVac and Wenesco that Mike used. They use a boot to funnel the solder to the component to be soldered. * Programmable head type [ie, ERSA, StreckFuss, Seho, Pillarhouse] is about the coolest thing to come out of Euroland since the pencil. The head moves to the component, fluxes the area, and squirts solder on the solderable surfaces. [Not as facile of a description as a sales type might give, but you get the idea.]

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Steve

#17921

Through-hole/SM mix | 16 October, 2001

Thanks for all of your suggestions.

Since there are quite a few options, the selected method will depend on volume, tolerated cycle time, ROI, etc. I believe we will be dealing with relatively low volume, so I am going to investigate the selective wave solder route.

Thanks again, Steve

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