here are certain timeless truths when it comes to printed circuits, and the more we stray from them, the more fervent our reaction when rediscovering them. Electrochemical deposition is going through such a revelation utilizing pulse reverse waveforms.
Electroplating was developed as a combination of Direct Current (DC) and a chemical bath. It was understood that this simple waveform and bath composition had considerable limitations. Numerous innovations followed to optimize the plating process for the desired deposit characteristics. There were advances in cell geometries, anode materials, temperature controls, monitoring, instrumentation and numerous others.
A key advancement was the use and optimization of chemical additives for the DC electroplating bath. We recognize the need to change our bath (electrochemical process) based on the required deposit characteristic (i.e. throwing power, flatter deposit, conductivity, etc.). Additives change the process parameters and mediate the desired results.
Performing the electroplating operation as a process (sequence of steps) enables us to properly level complex parts (such as PCBs) and achieve otherwise difficult deposit characteristics. For example, at a specific point during electroplating, we need to utilize an exact quantity of a specific additive. A second example is to stop the plating process, mask the section which was just plated, unmask another section to be plated in the next step of the process, and continue on. The point is that electroplating was developed and successfully utilized by creating processes. A process allows the user to accomplish the task by performing multiple measurable steps each specifically defined to yield a desired result. The sum of the incremental steps is a completed process with a desired result.
The timeless truth I referred to in the subhead is that “electroplating needs to be viewed and executed in terms of processes, regardless if it involves DC or pulse waves. This is especially true as our work pieces are composed of multiple geometries (fine-line traces, vias, PTHs) requiring multiple deposit characteristics.”
Somewhere in our search for continuous improvement, six-sigma quality, and reduced cycle time, we discovered pulse plating and forgot that timeless truth. Thus began our search for the “magic pulse waveform.” You know the one. You set your dials on this waveform and electroplate fine-lines, plated though holes (PTHs) and blind vias with bright deposits and high conductivity using any proprietary chemistry and additives developed for DC. The only reason we cannot find the magic pulse waveform is that those who have it will not share the information with us. We keep looking and waiting for someone to demonstrate it so that we can upgrade our plating operations.
We would not attempt to drill different sized holes with a single drill bit. Nor should we attempt to electrochemically fill different sized holes with a single pulse waveform. This approach is similar to our ancestors frustrated search for the mythical fountain of youth; they returned after several centuries with increased value placed on the old knowledge. Prior to the search for the fountain of youth, that knowledge consisted of a healthy diet, genetics, hygiene and exercise, to name a few.
Today we know to value diet, genetics, hygiene and exercise in the pursuit of a long and prosperous life. The pursuit of such ideal solutions is not itself bad; it motivates us to pursue a noble goal. What we find, however, may not be what we expected. In the pursuit of the fountain of youth, through medicine, technology and other efforts, we have in fact extended our life expectancy considerably, eliminated many deadly plagues, and are now stronger and healthier than at any other time in history. Clearly, we’ve not reached the ultimate goal, nor are our methods that which Juan Ponce de León expected to find in the 15th century, but it all adds up to a longer and more prosperous life.
Similarly with electroplating, as we search for a magic pulse waveform, we advance technology and solutions. This is not as effective as if we had the end goal in mind at the start, but it is progress, and these advances benefit our manufacturing capability and bottom line.
There are many modern examples to indicate that we will not find the magic pulse waveform, but rather, the need to incorporate new pulse technology with the old wisdom of performing the job as a process or sequence of steps. The sum of these tangible steps can yield a more efficient and higher performance process while providing time and cost reductions.
Faraday Technology, during IPC 2000, demonstrated a single waveform was not optimally able to geometrically level both PTHs and blind vias. This is important if we hope to reduce process time and cost by eliminating multiple plating baths.