Problem description: the customer will be our heavy gold PCB after welding, welding device is very easy to fall off.
Dongguan, circuit board factory attaches great importance to see at the time of the batch production records, find out the batch of inventory PCB empty plate, spray spray tin tin factory, to test the board on the tin effect, at the same time, sending an empty plate patch factory has lead and lead-free SMT experiment, test the actual effect of patch, the problem is not found.
Customer will issue board material sent back, we see the physical, indeed the device is very easy to fall off.
Fall off view point, there is a layer of dumb black substance.
Double-sided zedoary circuit board due to this bad phenomenon involves the circuit board surface treatment, solder paste, SMT reflow soldering and SMT surface technology aspects of process, in order to accurately find out the reason, we call zedoary factory, SMT factory, solder paste factory and our technology department to study together, where is what problem.
Problems cause analysis: we find inventory with the batch production of this circuit board.
Analysis experiment, in order to find out the problem: 1, the problem of plate of heavy gold slice analysis: 2, customer return circuit board remedial measures.
3, customer return circuit boards welding section analysis.
4, inventory board to return to tin tin factory, solderability test zedoary on
printed circuit boards.
5, inventory scrub brush solder paste, reflow soldering, the actual performance of weldability test circuit board.
Through a series of experimental analysis, and judgment, circuit board copper foil surface coated with a layer of nickel layer, and then a layer of gold on nickel layer on the sink, in order to protect the nickel oxide.
When patch welding, the first welding plate and a layer of solder paste, and solder paste natural penetration zedoary layer, and nickel layer contact (
Dumb black are the result of the solder paste and nickel layer effect)
, solder paste contain some active ingredients, reflow soldering, when welding the temperature reaches the temperature of the solder paste melting, with the help of the active ingredient, tin compound layer with the layers of metal (
IMC）
。
Customer return the plate due to the welding, the welding plate surface conditions do not meet the welding requirements, such as do not meet the reflow temperature (
The northern low temperature, preheat is insufficient, the actual temperature with the temperature table)
And the activity of solder paste,
Solder paste storage conditions)
, stencil thickness, leading to a nickel layer to form metal combined with tin, lead to device loss.
More regret two things: A, SMT production batch board, without the examination of the first plate production, to found the problem again, all done very trouble.
B, solder paste containing the active ingredient in the first time of reflow soldering effect at high temperature and evaporating, did not form effective alloy layer, high temperature welding again, effect is not obvious, to remedy adverse conditions.
Provisional remedies: because it is a heavy gold PCB batch plate, hand soldering iron repair welding and repair welding with a heat gun manual don't have the actual operability.
So though useful, but cannot solve the problem.
Improve furnace temperature, reflow soldering, anew despite losing solder paste resistance welding active ingredients help, but under the enough high temperature, also can form a metal compound.
As for the effect and heat loss, need to please customers own scale.
We tested not fill brush flux under the condition, the problem of customer return board, 265 degrees to reflow soldering once, results show that the device will fall off.
Adjust the reflow soldering temperature to 285 degrees, once again the reflow soldering.
Results show that the device will fall off.
Improve the reflow soldering temperature to 300 degrees, again once again reflow soldering, welding solid results.
Problem of plate will fill brush flux effect better?
If the customer need, we can arrange SMT factory do the test again.
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