Application of ferrites by electrophoresis process as keepers on printed circuit wiring of thin-film memories

A process for applying coatings to conductive materials by means of electrophoresis has been used for coating ferrites on printed circuit conductors as a magnetic keeper material for cylindrical thin film wire memories. This process is also known as electrocoating when used in this manner. The advantage of this process is the ability to obtain consistently a uniform coating of predetermined thickness and density on parts of any configuration. Another feature of this process is that good adhesion of the ferrites to the conductor is obtained. This is accomplished by use of a heterogeneous nitrogen resin as a suspension media for ferrites in an electrocoating bath The thickness of the coating increased with voltage and the density of the ferrites in the coating was dependent upon the concentration of ferrites in the coating bath. The denser the ferrites the higher the permeability. Word straps on a small piece of tunnel structure were electrocoated. Evaluation of these coatings were made in a cylindrical thin film tester. The keepered word straps had a much wider operating margin and a lower write threshold than unkeepered word straps. Complete units were then selectively keepered by this process and tested. These units were compared to those keepered with ferrite sheets and without keepers. The results of these tests indicated an overall improvement in the performance of the discrete keepered wire memory, i.e., lower word drive current, lower write threshold, improved adjacent bit disturb threshold, and increased output voltage with noise and cross talk levels of the discrete keeper lower than those with sheet keepers.