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Through-hole Connector Wave Solder Questions

Dave G

#18933

Through-hole Connector Wave Solder Questions | 20 February, 2002

I have some interesting problems on my hands that some of you may know the answers to. I am currently wave soldering a through hole connector to a rigidized flexible circuit. This is a compliant pin connector that is supposed to be pressed into a hardboard and not wave soldered at all. Because our flex is only .050" thick, we had to open the through-hole and solder it. Oh, and we have to use no-clean flux as well (my first experience with it). This leaves me two issues that are currently happening:

1. I am getting bridging between at least 2 of the pins on 75% of every trailing edge. The pitch between the closest pin is .055" and my stick through is .025". My pads are .038" so I tried adding solder thieves that were .050" behind them. Before I added the thieves, we were getting 100% bridging on every connector. My thoughts were to make larger thieves or possibly reduce the stick through by increasing my rigidizer (FR4) thickness. Any design or process ideas?

2. Because it's flex, I also have to use carrier pallets. Due to a feature on the connector, the opening in the pallet comes extremely close to the closest pad (.020" on one side) and I'm getting voids only along that edge. We currently spray flux and it appears there is proper distribution of the flux, but I'm not sure what this close pallet feature is doing to those pads during (IR) preheat and in the solder itself. Is this shadowing? Is the flux burning off or is this pallet feature robbing heat from these pads? I can't clearance the connector any further. Any help is appreciated, I'm a bit of a rookie. Thank you in advance!

Dave

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#18935

Through-hole Connector Wave Solder Questions | 20 February, 2002

THIEVING * Layout: I�d guess the surface area of your thieves is not large enough. The pull from the thief is not great enough to over-come the pull from the connector pins and pads. Consider tripling the size of the thief. As you say, reducing the stick through by increasing the rigidizer thickness will also help. * Process: Keep your pot temperature up. Our old friend J Thorup says solder gets "sluggish" and bridging increases when lower than 470-475�F.

SOLDERING * Fluxing: It could be tough to get flux between the tall connector pins and the walls of the opening in the pallet. Plus your NC is probably lame. * Preheating: Tough to say if you�re burning-up your flux or not preheating enough to compensate for the pallet. [Probably the latter.] Try measuring the temperature on various connector pins to get a better understanding of temperature differences. * Voiding: Voiding in wave soldering is peculiar. It almost always has to do with moisture contained within the board, but that is probably not so in your case, because the voiding is localized along the pallet. It could be this voiding is a result of either improper flux activation during preheat or excess flux puddling-up in the space between the pallet and the flex. [Leaving excess NC flux on aboard is as dangerous as leaving water washable flux on the board.]

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Vince Whipple

#18942

Through-hole Connector Wave Solder Questions | 21 February, 2002

Hi Dave G, This is an interesting problem.. I can only add the following: - Try trimming the pins and see it this helps.. sometimes the decreased surface area will lessen the surface tension enough to minimize the effect of bridging. - As Dave F was pointing out, an accurate read of the temperature is important. This is especially true with NC. Remember with a NC, the 4 most important things when spraying are Temperature, Coverage, Temperature, and oh yeah, TEMPERATURE.

For the bridging / voids, these issues may be related and hit in the following manner: - If there is enough slop in the pallet, try moving the flex away from the the close edge of the pallet. If this alleviate the problem it may point you in a direction for an interim solution. - Try playing with the speed of the wave at the back dam.. Faster, slower. don't cheat by just adjusting the pump RPMs, adjust the dam also ( make sure you don't introduce turbulence in the wave). Sometimes the pallet interface to the board will cause a temporary increase in wave speed. this increased speed maybe causing the problems described. << do the last one on a weekend. It may take a while to work out other problems that it creates. Good luck, Vince W. vwhipple@sono-tek.com

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