PCB News - Immersion gold circuit board welding components fall off

Immersion gold circuit board welding components fall off

After the customer soldered our company's gold circuit board, the soldered device is very easy to fall off. Shenzhen circuit board manufacturers attach great importance to checking the production records of the batch at that time, finding out the empty boards of the stock circuit boards of this batch, and sending them to the tin spraying factory to spray tin to test the tinning effect of the boards, and at the same time, send the empty boards The patch factory did lead and lead-free patch experiments to test the actual patch effect, and no problems were found. The customer sent the problem board back in kind, and we checked the real thing, and it was true that the device was very easy to fall off. Check the falling point, there is a matt black substance.

Because this undesirable phenomenon involves the surface treatment of the circuit board, solder paste, reflow soldering and SMT surface mounting process and other processes, in order to accurately find the cause, we convened the sinking gold factory, the patch factory, the solder paste factory and The craft department of our company will study together to find out what the problem is.

Problem analysis:

Our company found this circuit board produced in the same batch in stock. Do analysis experiments to find out the problem:

1. Immersion gold slice analysis of the problem board:

2. Remedial measures for the circuit board returned by the customer.

3. Analysis of the soldering section of the circuit board returned by the customer.

4. Return the stock board to the spray tin factory to spray tin, and test the solderability of the immersion gold on the circuit board.

5. Brush solder paste on the stock board, reflow soldering, and test the actual solderability of the circuit board.

Through a series of experimental analysis and judgment, the surface of the copper foil of the circuit board is plated with a layer of nickel, and then a layer of gold is deposited on the nickel layer to protect the nickel layer from oxidation. During patch soldering, first put a layer of solder paste on the pad. The solder paste naturally penetrates the gold-immersion layer and contacts the nickel layer (the dull black is the result of the effect of the solder paste and the nickel layer). The solder paste contains some active ingredients., When the temperature reaches the melting temperature of the solder paste during reflow soldering, with the help of the active ingredient, the tin forms a metal compound layer (IMC) with each layer.

The board returned by the customer did not meet the soldering requirements at the time of soldering. For example, it did not reach the reflow soldering temperature (the northern temperature is low, the preheating is not enough, the actual temperature is inconsistent with the temperature zone table), the activity of the solder paste (tin Paste storage conditions), the thickness of the steel mesh, etc., caused the nickel layer to fail to form a metal compound layer with tin, resulting in the device falling off.

There are two regrets:

A. During the batch production of board placement, the first board production inspection is not carried out, and it is very troublesome to find the problem after all of it is completed.

B. The active ingredients contained in the solder paste produce an effect and volatilize when the high temperature of the reflow soldering is performed for the first time, and an effective alloy layer is not formed. The effect of high-temperature soldering again will not be obvious, and it will produce unfavorable conditions for the remedy.

Temporary remedial measures:

Because it is a batch of immersion gold circuit boards, manual repair welding with electric soldering iron and manual repair welding with hot air gun are not practical. So although useful, it cannot solve the problem.

Increase the furnace temperature and reflow soldering. Although the help of the solder resist active components in the solder paste is lost, a metal compound layer can also be formed at a sufficiently high temperature. As for the effect and high temperature loss, please ask the customer to balance it.

We tested that without repainting the flux,

The problem board returned by the customer was reflowed at 265 degrees, and the result showed that the device would still fall off.

Adjust the temperature of reflow soldering to 285 degrees, and perform reflow soldering again. The result shows that the device still falls off.

Increase the reflow soldering temperature to 300 degrees again, and reflow soldering again, the result is firm soldering.

Will the effect of repairing the flux on the defective board be better? If the customer needs it, we can arrange the placement factory to do the test again.