PCB " short circuit " is a question of each PCB manufacturers will encounter almost every day , and it is a difficult problem , improve the well or bad this problem is directly related to the cost of production is low or high , the pass rate is also related to the finished product problems.
Now the reasons causing these phenomena individually analyzing and improving methods listed below:
First, run a short circuit caused by tin
1, in the back caused by improper operation of the membrane tank ran syrup tin ;
2 , the film has been retired due to run tin plates stacked together .
Improvement:
( 1 ) . Stripping syrup high concentrations , retired film for a long time , anti- plating has already dropped, board still alkaline solution to soak , some tin foil attached to the surface of the powder , a metal tin guarding a thin copper surface etching , played the role of corrosion , resulting in the removal of copper is not in addition to clean, leading to short-circuit . So we need to strictly control the concentration of membrane syrup retreat , temperature, film back time and time back flapper film frame plugged in, not laminated together between the board and the board touch .
( 2 ) the back sheet film drying will not superimposed together such immersion tin plate between the plate and the film was not dried back , some of the tin layer on the copper foil attached to the surface is dissolved when etching a a thin layer of metallic tin patrol copper surface , play a role in corrosion , resulting in the removal of copper is not in addition to clean, leading to short-circuit .
Second, the net result of a short circuit is not etched
An etching solution parameter control directly affects the quality of the etching , the current Division I use alkaline etching solution , specifically as follows :
1.1 PH value: 8.3 to 8.8 between the control , if the PH value is low , the solution becomes a viscous state, color whitish , Etching rate decreased , this likely to cause side etching is controlled primarily by adding ammonia PH value.
1.2 chloride ions: controlled between 190 ~ 210g / L, chlorine ion content mainly controlled by the etching salts, ammonium salts are etched and supplements thereof.
1.3 Specific Gravity: primarily by controlling the content of copper ions for control of the proportion of the general control of the copper ion content between 145 ~ 155g / L, each producing about an hour once for testing in order to ensure the stability of gravity .
1.4 Temperature : Control at 48 ~ 52 ℃, if the temperature is high ammonia volatilization fast, the pH will cause instability and cylinder etching machine are mostly made from PVC material , PVC temperature limit is 55 ℃, Above this temperature is likely to cause cylinder distortion, and even cause etching machine scrapped , it must be installed with an automatic thermostat temperature for effective monitoring to ensure that within its control in .
