Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

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gold connectors


RDR

#20131

gold connectors | 29 May, 2002

We are starting to see a large increase in the use of through board gold plated connectors that require hand soldering with the limitation of .o6" encroachment up the pin. What is the best way to accomplish this? we currently scrap about 5-10% of these connectors from capillary action errant irons etc... Russ

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#20139

gold connectors | 30 May, 2002

Hello Russ,

I'm not quite sure I understand your question. Are you saying that you must hand solder these connectors because the gold plating doesn't allow other though hole processing methods to wet the solder the length of the pin in the PTH?

Regards Jim Zanolli

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#20140

gold connectors | 30 May, 2002

I assume the connector is like one used in PC104 that allows mating of boards together by inserting the pins extending from the connector on one board into the female portion of the connector on a second board.

Who ever accepted this job is dopey. The ol' 'I shot it, you skin it' approach. Not a good way to run a business. What you are doing has serious problems for two reasons: 1 Hand soldering connector is almost impossible to do reliably. 2 Trying to restrain solder flow like you describe is very difficult, expensive, and makes it even harder to make good solder connections.

If you want to continue on this path, consider dipping the pins of the connector in temporary solder mask, soldering the pins, and removing the mask. In fact, if you take this approach, you could wave solder the connectors.

If you want to make your life better [and more importantly make your operators' lives better], consider changing to press fit connectors. Search the fine SMTnet Archives. We: * Taked about gold press fits on HASL boards here on SMTnet recently. * Have talked about press fit connectors generally several times on SMTnet.

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#20154

gold connectors | 30 May, 2002

Hey Jim,

What can you tell us about the causes, results, and prevention of 'fretting corrosion' in connectors?

Jim, I'm not adding this to insult you, but as a source of more information for those that are not familiar with the topic. Background on fretting corrosion: * http://corrosion.ksc.nasa.gov/html/fretcor.htm

* http://www.corrosion-doctors.org/Forms/fretting.htm

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#20158

gold connectors | 31 May, 2002

Hello Dave,

As related to connector mating interface, fretting corrosion is the oxidation of the contact points, causing high resistance across the interface. Fretting corrosion is caused my micromotions in the interface exposing the metalized contact interface surfaces to ambient air. The micromotions are caused by vibration and temperature cycling.

As an examples, roll your hands into a fist and bring the fists together. Roll you hands back and forth. This simulates micromotion movement of contact interface "A spots" or asperities. What then happens is the exposed A spots can oxidize to the point that when micromotions move them, they will end up with oxidized A spots from both sides of the interface in contact with each other, causing higher resistance.

Fretting corrosion is typically a problem with connector mating interfaces with non-noble metal plating, such as tin or tin-lead. Higher contact normal forces (2-5 times higher than gold-gold) can provide a reliable tin-tin interface. Lubrication also helps non-noble metal interfaces. Of course you can never go wrong with a relatively thick (15 microinch) gold to gold interface.

Best Regards Jim Zanolli

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RDR

#20160

gold connectors | 31 May, 2002

Dave, you would be correct in this application. I wish I could prevent these products from coming into our shop, but... I do like the idea of press fit and I will have to research on the availability and persuade the customers to change. I was wondering if anybody heard of or manufactures a "boot" to apply to these connectors prior to soldering. Would anyboby also know of a good temp mask that can be used for this application (needs to be thin, watersoluble, and dry quickly)

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RDR

#20161

gold connectors | 31 May, 2002

Jim, you are right in this. these connectors have long pins 1/2" or so that protrude through the board and are used for mating into a female connector on some other assembly. due to both length and "no solder allowed in contact area" criterias these need to be hand soldered.

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#20164

gold connectors | 31 May, 2002

Russ We decided to use a PC-104 brd for a piece of equipment and had to make a "PC-104 Adaptor Brd" as it is affectionately known. The actual PC104 connectors came with what they called a solder system, a flat piece of solder with holes in it that was placed on the connector prior to it being placed on the board. We initially had problems with bridging under the connector but for the most part it worked. http://www.commcon.com/main/

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#20173

gold connectors | 31 May, 2002

We use boots / shunts er wutt ever you call them to protect solderable component surfaces from wave soldering. Not sure how it would work in your case try: * Kinnarney Rubber 450 Main St. P.O.Box 37 Mantua, N.J. 08051 609-468-1320 fax 7438 http://www.kinnarney.com/ Jim Kinnarney

On temporary mask, try: Saati America [800-766-3676]. The product name is Dorn Temporary Solder Mask. It is actually manufactured by Cerulean Blue Ltd. [206-525-8992].

This used to be Alpha Metals HV-110 that was the screenable version of their 110 water-soluble temporary solder mask / resist product family. The temporary solder mask / resist does not contain insoluble fillers such as clay, fumed silica etc, which can clog wash nozzles build up in tank sumps or wear out pump seals on aqueous washers.

Another is: Wondermask [Techspray, #2207-p] 2207G

Be careful. Both 110 and Wondermask are highly ionic and are SIR killers.

Considerations is selecting temporary mask are: * Method of application: screen print, auto-dispense XY system, hand application, etc. * Type of material: filled / unfilled, water base / alcohol base etc. * Type of cure * Type of washing equipment/chemistry * Assembly compatibility SMT-wave solder-mixed technology need to be considered for material choice. * Board features to be masked: large features, cut-outs, melting metals etc. * Applied mask shelf life and storage: masked board storage conditions, method of storage, hold times prior to use etc. * Humidity, how boards are stored [i.e. wrapped/unwrapped, slip sheets, flat stacked/edge stacked, etc] * Hold times greater than three to six months can all influence the ability of the material to perform correctly.

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