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Resistor Paks on solder side of board

Tekguy2000

#6380

Resistor Paks on solder side of board | 20 July, 2000

We are currently running boards with resistor paks on the solder side of the board introducing these to the wave solder. We cannot get rid of shorting between the leads. We are using a water soluble acohol based flux. The option of going to selective pallet is not an option due to redesign criteria. My keep out areas are too close without changing design. Looking for any suggestions short of keeping them off of the bottomside.

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Bob Willis

#6381

Re: Resistor Paks on solder side of board | 20 July, 2000

By resistor packs do you mean SOIC resistor networks ?

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Boca

#6382

Re: Resistor Paks on solder side of board | 20 July, 2000

I am not answering for Techguy2000, but I am chiming in here, I have the same problem.

Our resistor packs are ceramic body with no leads, they have a metalized area reminicent of the old castelation leads of year gone by. The lead pitch is 50 mils on some and even less on others. They are becoming quite popular with some customers and a real problem in wave soldering.

We use OA flux, 2 stages of preheat, we hit the flux manufacturers temperature targets. We use a turbulent wave, lambda wave and Hot Air Knife (Electrovert machine). We see both 'missing' and 'bridging'.

I recommend new designs move them to the top side of the fab.

Any suggestions?

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Bob Willis

#6383

Re: Resistor Paks on solder side of board | 20 July, 2000

If you are getting skips on these parts the most common reason for skips is gassing and wave too low. I would agree that wave soldering these parts is not ideal.

If the shorts are always in the same location on one or two pins a glue dot done during placement between the pads solves the problem. I don�t believe a air knife would remove the shorts on these parts. You may well agree.

Don�t worry about jumping in I just want to go and get a glass of wine !!

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Tekguy2000

#6384

Re: Resistor Paks on solder side of board | 20 July, 2000

These parts are flat chip resistor arrays that have 4 end terminations on each side. It looks liek an IC but is typically in an 0805 and 1206 package type with convex terminations. .031" pitch from termination to termination and .011" spacing between termination. Part height is .021". We are using the same set-up and wave as Boca (air knife, wave parameters, etc) Electra. I have not to this point emplemented any thieving pads which may be an alternative but have minimum spacing requirements due to mass and via placements. I have several boards with these on the bottom with up to 31 per board. I have plotted the defects from build to build and it is random, but there are more shorts in some areas than others. I tried to determine if this was heat related due to inner layers but there doesn't seem to be any coorelation.

Are you listening to Curtis Mayfield while sipping your wine?

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Bob Willis

#6385

Re: Resistor Paks on solder side of board | 20 July, 2000

Based on what you have said so far it would be worth trying extra pads and as you may know the drainage pads should be a minimum of three times the length of the pads before them to be effective. Also take some parts stick them to a glass plate and run them through the wave and see how they drain.

Next take some repair pads, the stick on pads to create dummy pads on the glass and see the effect again when you run it through the wave

No Curtis Mayfield is not on the CD at the moment my other half does not rearly like the sweat tones of Mayfield. For you interest my girl favourate is Ann Peebles. The girl who sang the song "I am going to tear your play house down"

Bob

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