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Solder climbs on the lead and touches the body of the component

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#72100

Solder climbs on the lead and touches the body of the component | 12 May, 2014

Hello all,

I have a diode(gold plated)on some assemblies that gives me a a hard time. The paste is wetting too good and climbs the lead of the component and touches the body which is a defect. I just wonder what if there is a way to heat the board earlier that the components leads and make the solder sticks more to the PCB than to the leads of the component? some of the pads are probably bigger than they should be(more paste on these apertures), but at this point I don't want to recut 20 stencils. Any thoughts are appreciated. Process is leaded.

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#72101

Solder climbs on the lead and touches the body of the component | 12 May, 2014

It sounds like a bit too much solder on the PWB, caused by too large a pad for the lead it will contain.

In that case solder reduction is the way to move forward. What are the options there? 1. New stencil or stencils - (not desirable) 2. Increase blade pressure at print to reduce solder print (keeping in mind that this will occur all across the board. 3. Change in paste type can effectively reduce the amount of metal in the joint. For example, moving from a type 4 to a type 3(again, global across the board, keep in mind the rest of the components and their respective joints.) 4. Mask your stencil, and hand solder that part as a separate process.

Stencil change is probably best, but I completely understand not wanting to change them (all) out.

Best of luck, let us know how you solve this! 'hege

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#72102

Solder climbs on the lead and touches the body of the component | 12 May, 2014

Hi Evtimov

'hege gave you a plausible explanation for what's going on with solder running-up the lead of your components: TOO MUCH METAL!!!

I've got different one. This explanation goes along the way that you're thinking, but just opposite. The reason solder is running up the leads of your component is: Component lead is much hotter than the pad. Solder will always run to the heat.

That you are getting good wetting to the pad tells me that you don't have a contamination issue. You just have your heating recipe out of wack. I'd guess that the leads where you have this issue are sitting on pads that sink more heat than you'd expect them to sink. Since you're getting good pad wetting, you're not off by much.

Prove I'm correct by measuring the temperature on both the lead and on the pad when you run your approved product thermal recipe.

If that's what's going on, figure out how to put more energy into the board than you are now. * Slowing my conveyor would be the first thing I'd try. * Maybe messing with preheats would help.

BR ... davef

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#72104

Solder climbs on the lead and touches the body of the component | 12 May, 2014

Thank you guys. As we are speaking I keep examine the problem and here is what I got so far. 1. I measured the temperatures on my profile and the lead is hotter than the board. The lead goes 12 seconds earlier than the pad and is taking the solder. I tried to keep my lower zones hotter than the upper ones but that helped just a little bit. Still the lead is hotter than the PCB(just as DaveF suggested) 2. I started to tape my aperture on the stencil and just after I reduced 75% I got a good result(as Hege suggested).

It looks that paste reduction will fix it, so I will make calculations and will recut at least one stencil to see the repeatability of the process. Fixing the profile looks to be hard to get it there. DaveF I think that this pad is really absorbing a lot of heat as you said and I couldn't get it close to the temperature of the leads.

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#72117

Solder climbs on the lead and touches the body of the component | 14 May, 2014

Dave is touching on one of those magical things that keeps us process engineers well paid and dancing (Well, some of us, lol). Heavy boards with light components. Solder Follows heat. Component heat up earlier. Repeat, Solder follows the heat. Careful oven control can help to mitigate this, but for me, this kind of oven control is a fine tuning detail. To get to the guts of this one, and due to the gross initial change required, I was thinking metal reduction first! 'hege

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