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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

lead substrate materials

Bob Smith


lead substrate materials | 29 January, 2002

Can someone tell me what metal substrates are comonly used for component leads with gold plating? If the gold plating is missing, are any of the substates incompatible with 63/37 solder? Thanks.

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lead substrate materials | 29 January, 2002

Please help us understand your situation better by describing the following: * Component [ie, PTH/SMT, type of component, lead finish you expected/ received, etc.] * Board type [ie, type of board FR-4/CEM/ceramic, etc.] * Solderability protection on pads [ie, hot air solder leveled, gold over nickel, etc.] * Solder mask on board * Solder used * Soldering process

When you say, �If the gold plating is missing�, what gold plating are you talking about � * Component leads * Solderability protection on the pads on the board * Er, what

Continuing, when you say, �If the gold plating is missing�, what is in place of the gold plating? Does this replacement surface accept solder?

Commonly, when we talk substrate, we talk �

Substrate. Base Material. A supporting insulating material upon which parts, substrates, and elements are attached. Base Material. Substrate. In printed circuit board fabrication, the insulating laminate on which the conductor pattern is formed. The base material may be rigid or flexible.

So, when you say, �� what metal substrates are commonly used�, we scratch our heads. Not to say no one uses metal substrates, but they�re no common. Help us understand your question better.

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Bob Smith


lead substrate materials | 30 January, 2002

Hi Dave,

Sorry about that. Specifically, I am referring to radial leads on a crystal. The leads are supposed to be gold plated but only 1/2 to 2/3 of the lead is plated. We bend the lead to form a foot which is soldered to a pad on the PCB. Normally we would reject the lot but these are custom made and we are in bind for time and would like to use them if possible. We experienced solderability problems with the crystal lead when we tried a sample but dipping in a solder pot may solve that problem unless the metal the gold is deposited on is incompatible with 63/37 solder. I would like to evaluate long term reliability.

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lead substrate materials | 30 January, 2002

The gold is compatible with your solder. Gold will dissolve in your solder very quickly. Assuming you have a fairly large [~ couple hundred pounds] solder pot, the gold will not, over the short term, affect the performance of the pot.

The issue is not the gold. The issue is the corrosion of the material [nickel?] underneath the gold. In real life, you do not solder to gold. Gold dissolves in the solder and you solder to the surface under the gold. The gold protects that solderable surface from corrosion.

I�d guess you are in deep dudu. Guessing at what�s going on: * Supplier plated the gold solderability protection thinner than expected. * Thin gold allowed the under-plate, below the gold, to corrode. * Flux that you are using does not have enough stomp to remove that corrosion. * Solder does not flow.

Consider talking to your flux supplier about a BIG flux.

Talking to your reliability concerns about removing the gold in a solder pot and then soldering, that�s what you should be doing in the first place. Check J-STD-001, 5.4.1 � Gold Removal.

As an aside, er, maybe continuing with the J-STD-001 thought, too much [GT 3-5% weight] gold in an eutecticish solder connection can cause brittle solder connections.

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