IMMERSION SILVER

Immersion silver is another finish prospect. Silver is one of one of the most conductive aspects. Even its oxides are very conductive, yet regrettably are not as conveniently solderable. There are additionally long-lasting concerns over silver movement. Strides appear to have been made recently to address both issues. Immersion finishes as slim as 0.3 mm appear to be capable of keeping solderability and then have actually the added advantage of being wire-bondable making use of light weight aluminum cable ultrasonic bonding methods.

ELECTROLESS NICKEL IMMERSION GOLD

Electroless nickel immersion gold (ENIG) finishes have been the subject of countless study documents in recent years. They have actually been postured as a cure all of kinds, offering in a single coating, planarity, solderability, wire bondability and a corrosion-resistant contact finish, so all the initiative to make them function accurately comes as not a surprise. What has actually been troublesome is the sporadic incident of the black pad phenomenon in which solder leads lift away from what was the nickel-gold user interface. Nevertheless, some study has suggested that a higher percent of phosphorous in the nickel could ease the trouble.

Immersion gold utilizing the ENIG procedure is usually 0.1 µm to 0.2 µm thick as well as not fit to gold ball bonding or several insertion links, making electrolytic gold one more option. For gold sphere bonding, a thickness of ~ 1.0 µm has actually verified appropriate. Soft gold with a firmness of approximately 90 Knoop is liked. For calls, hard gold plating is chosen. Electrolytic gold requires that electric links exist and then shorting bars are typically made use of to this end.

DIRECT IMMERSION GOLD (DIG)

Another finish that has obtained some attention is direct immersion gold (DIG). DIG has the advantage that there is no nickel plating needed, making it a simpler process. Immersion coating of gold straight over copper is a basic procedure due to the fact that both metals are far apart in the electromotive collection. Gold will conveniently replace copper, however the density is restricted by diffusion to less than a micrometer. The one large downside is that gold is currently hovering around $1500 per troy ounce, making it a pricey and also less attractive solution.

NATURAL SOLDERABILITY PROTECTIVE COATINGS

Organic solderability safety coatings (OSP) have a long history, going back almost to the start of the PCB sector. The current class of coatings is much superior to the earlier materials. Newer coatings fast and also simple to apply as well as have been created to endure numerous travel through assembly while shielding and keeping the solderability of the copper they coat. OSPs have succeeded for traditional solders, but some concern has been revealed concerning their capability to endure as several passes in flex PCB lead-free processing.

Finish options are plentiful to fulfill the different requirements of the myriad of applications that flex PCB now serve. In addition to the options listed, there have been some interesting layers based upon nanotechnology that have been seeing some higher use. Nevertheless, with no true remedy in the mix, the option needs to be made based on the assembly and usage standards of the design.