Electroplated Copper Interfacial Micro Void Nucleation Control
Controlling copper interfacial micro-void nucleation requires balancing plating bath organic additives, limiting total organic carbon, and enforcing slow thermal anneal ramps.
Organic Inclusion
Meaning
Entrapment of non metallic additives within a plated metal layer occurs when brighteners or levelers become physically buried during the deposition process. This organic inclusion happens most frequently in high current density areas where the metal ions arrive faster than the organic molecules can desorb. The resulting deposit contains carbon, sulfur or nitrogen atoms that were never intended to be part of the metal matrix.
Material Properties
The presence of these foreign atoms alters the physical behavior of the copper traces. High levels of organic inclusion increase the internal stress of the deposit, making the metal harder and more brittle. This brittleness can lead to cracks in the plated through holes when the board is exposed to the heat of a soldering iron.
Purity Measurement
Analytical techniques like secondary ion mass spectrometry reveal the concentration of trapped species. While some organic inclusion is inevitable in bright copper plating, excessive amounts indicate an imbalance in the bath chemistry. Manufacturers monitor the ductility of the plated copper to detect when the levels of trapped organics have exceeded the safe limit.
Process Prevention
Adjusting the current waveform and maintaining the correct additive concentration limits the capture of these molecules. Using pulse plating instead of steady direct current can help reduce organic inclusion by providing time for the additives to redistribute on the surface. Lowering the brightener concentration to the minimum effective level also minimizes the risk of entrapment.