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Connector solderability

#22272

Connector solderability | 5 November, 2002

This one's got me stumped, so I thought I'd throw it out for discussion: I have a 20 pin SMT ribbon connector by Molex that I've been using for about a year without problem, but recently things aren't looking so good. The solder is pulled up off of the pad and onto the lead of the connector. There are 6 connectors per board and the defective joints are random among the connectors. Adjacent joints look just fine. But (get this) only one side of the connector is affected. The other side is always ok. I've checked the print, checked the profile, ran the board backwards to see if anything has changed and other things that I can't think of right now. The boards are HASL and I'm using an OA paste by OMG Americas. Everything else on the board looks great. The defective joints can be touched up with an iron without problem. Any ideas?

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RDR

#22274

Connector solderability | 5 November, 2002

This sounds like a contamination issue with the HASL finish.(solder on lead but not on pad). I have experienced this before and it was related to the HASL process at our supplier. They found some type of contaminate in the bath (unfortunately I cannot remember what it was). On another note, My experience has shown that OMG paste is not always consistant in regards to activity (wetting) and I have recently switched to another supplier for that reason. It doesn't sound like this is your problem though. Are you processing these assemblies through a wave process? I have seen in some cases where the wave will heat the boards and components and then the board cools off faster than the part (or something like that) and the solder dewetts off of the pad and collects on the lead. Could it be possible that this phenomena may be happening in a reflow process? I would assume that this defect is noticed immediately after reflow?

Russ

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#22284

Connector solderability | 6 November, 2002

This defect is there after reflow. My first thought was that the boards had some sort of contamination, too. This is a new PCB manufacturer for this board (they have been making other boards for us). But... why only on the connectors -- why only on one side of the connectors? I thought that maybe the connector reached reflow before the board and pulled the solder off of the pad. I ran a profile to see if this may be happening. It looks ok but I question my measurements because the connector is already soldered (heatsinked) to the board in my test. I'm running a Conceptronics convection reflow.

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#22287

Connector solderability | 6 November, 2002

First, from what you say, it's unclear that there is a "solderability" issue with your connectors. Different appearance of the soldered connection from one side of the connector to the other is what we're talking about [I think].

But it is curious. The next thing to consider is measuring the reflow temperature on "good" and "bad" pads. [Probably see no difference though.]

If that doesn't point you in a proper direction, consider that there maybe something screwy in the fabrication of the component, say, like something that causes leads to lift differently during the thermal cycle. Investigate this alternative by watching the leads move while heating the component on a hot plate. Recognize that the hot plate does not represent your oven well, but may give you a direction to head in your investigation.

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#22296

Connector solderability | 6 November, 2002

Nothing funny seems to happen to the connector when heated. I have no idea how to monitor the temperature of a good pad vs. a bad pad because I have no idea before reflow which ones will be good and which will be bad. I did take a board and rip the plastic off the connectors leaving the metal strips that form the legs/pins. On initial inspection, it appeared that the solder disappeared. With careful examination, the leg is coated in a very thin plating of solder. I can't believe that it whetted that well. Usually when the solder won't whet the pad, it forms a clump on the lead - easy to spot. What do I do, complain to Molex that their parts take solder too good???

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#22300

Connector solderability | 6 November, 2002

I hear you on the profiling issue. That won't get at the issue any how.

Your observation of solder wetting confirms that solderability is NOT the issue.

You may be seeing a "cold solder connection". The issue is the TCE of the different materials in the connector. OK, try this trick: * Find a bad connector. * Record the location of the bad pins. * Remove the connector. * Rotate the connector 180 deg * Resolder the connector. * Check the location of the problem pins.

Here's another one: What happens when you reflow the connector rotated 90 deg in the oven, as compared with rotating it 180 deg?

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