The volume of electronic products is becoming thinner and shorter. Directly stacking holes on through blind holes is a design method to obtain high-density interconnection.To do a good job of hole stacking, we should first do a good job in the flatness of the hole bottom. There are several manufacturing methods, among which the electroplating VIA copper filling process is a representative one.
Advantages of VIA copper filling
– It is conducive to the design of stacked holes and holes on the pad;
– Improve electrical performance and contribute to high frequency design;
– Helps to dissipate heat;
– Plug hole and electrical interconnection are completed in one step;
– The blind hole is filled with electroplated copper, which has higher reliability and better conductivity than conductive adhesive.
Physical influence parameters
The physical parameters to be studied include anode type, anode cathode spacing, current density, agitation, temperature, rectifier and waveform, etc.
(1) Anode type
When it comes to anode types, they are nothing more than soluble anode and insoluble anode.Soluble anode is usually phosphorus containing copper ball, which is easy to produce anode mud, pollute the plating solution and affect the performance of the plating solution.Insoluble anode, good stability, no anode maintenance, no anode slime, suitable for pulse or DC electroplating;However, the consumption of additives is large.
(2) Distance between anode and cathode
In the process of electroplating vias filling, the spacing design between cathode and anode is very important, and the design of different types of equipment is also different.No matter how designed, it should not violate Farah’s first law.
There are many kinds of agitation, including mechanical swing, electric vibration, air vibration, air agitation, jet, etc.
For electroplating hole filling, it is generally inclined to add jet design based on the configuration of traditional copper cylinder.The number, spacing and angle of jet on the jet pipe are all factors that have to be considered in the design of copper cylinder, and a large number of tests have to be carried out.
(4) Current density and temperature
Low current density and low temperature can reduce the deposition rate of surface copper and provide enough Cu2 and brightener into the hole.Under this condition, the hole filling ability is strengthened, but the electroplating efficiency is also reduced.
Rectifier is an important link in electroplating process. At present, the research on electroplating hole filling is mostly limited to full plate electroplating. If the graphic electroplating hole filling is considered, the cathode area will become very small. At this time, high requirements are put forward for the output accuracy of the rectifier.
The output accuracy of the rectifier shall be selected according to the product line and the size of the via.The thinner the line and the smaller the hole, the higher the accuracy of the rectifier.Generally, the rectifier with output accuracy less than 5% should be selected.
At present, from the perspective of waveform, there are pulse electroplating and DC electroplating.The traditional rectifier is used for DC electroplating hole filling, which is convenient to operate, but there is nothing to do if the plate is thick.PPR rectifier is used for hole filling in pulse electroplating, which has many operation steps, but it has strong processing ability for thicker in-process plates.