I'm sure you seldom hear the term of silver ion migration. As a professional sales person of toggle switch manufacturer, it's also rare to meet such requirements from this customer. Want to know why customers ask for it? Then we need to understand its principle and function first. Since we want to do this test, we must prevent some uncertain factors or product stability.

 

What is silver ion migration? Silver migration refers to the formation of hydrogen and hydrogen ions by electrolysis of water molecules penetrating into the silver conductor surface in a humid environment with a DC voltage gradient. Chemical formula: H20 → H + + OH -.

 

Under the action of electric field and hydroxyl ion, silver dissociates to produce silver ion, and produces the following reversible reactions:

 

Under the action of electric field, silver ions migrate from high potential to low potential, and form flocculent or branching expansion, and form black silver oxide on the boundary of high and low potential connection. The phenomenon of silver migration can be clearly observed by the famous water drop experiment. The water drop test is very simple. The phenomenon of silver ion migration can be observed by dropping water drops between the silver containing conductors close to each other and adding DC bias voltage.

 

The migration of silver ions will lead to the formation of bypass between the conductors without electrical connection, resulting in the decrease of insulation and even short circuit. In addition to the silver contained in the conductor component, the factors that lead to the silver migration are: substrate moisture absorption; DC voltage between adjacent conductors, the closer the conductor spacing, the higher the voltage, the easier to produce; bias time; environmental humidity level; the presence of ions or dirt adsorption; the characteristics of the surface coating, etc.

 

The failure of bypass caused by silver migration has the following characteristics:

 

In the case of high humidity and bias voltage, silver ions will leave residues between conductors after migration, and there will still be bypass resistance after drying, but its V-A characteristics are non-linear, unstable and non repeatable. This is similar to the case of surface contamination by conductive ions.

 

Silver migration is a well-known phenomenon in the industry, which is completely preventable: avoid high DC potential difference between adjacent conductors with fine spacing in layout and wiring design; make surface protection layer to avoid water vapor infiltration into silver conductor. The whole circuit board can be sealed or coated to protect the product in extremely harsh service environment (such as close to 100% RH, 85 ℃). In addition, cleaning the flux residue on the substrate after welding can also prevent the surface from being contaminated by conductive ions.

 

Silver ion migration test of toggle switch:

 

Silver migration test conditions: keep the switch in the normally open state, apply DC 35 V voltage between the normally open switch terminals and place it in the environment of 85 ℃ and 85% humidity for 120 hours. The judgment criteria are: there is no abnormality in the electrical and mechanical properties of the product; there is no mist on the normally open switch; there is no mist on the PCB surface between terminals (silver ion migration products).