Issue link: https://iconnect007.uberflip.com/i/521718
14 The PCB Magazine • June 2015 and C and D. With the addition of select stress reducing additives, labeled Electroless A, the stress of the deposit is reduced significantly. Electroless copper solutions containing ad- ditives from Electroless A in Figure 4 were eval- uated further to determine the influence on PCB reliability. Specifically, the resulting copper deposit's reliability was evaluated on intercon- nects within multilayer PCBs when exposed to thermal stress. Substrate was processed through these solutions and replenished accordingly with chemical components to maintain con- sistent operating conditions. Operating in this way allows the solution to increase in electro- less copper byproducts, such as formate, sulfate, additives, etc., similar to how commercial elec- troless copper systems are operated. In general, electroless copper solutions are controlled by analysis of the main chemical components as well as the specific gravity of the solution. As electroless copper solutions increase in specific gravity, undesired properties, such as solution instability, deposit defects, and byproduct for- mation, become more pronounced. Ultimately, represent materials that have shown poor cov- erage on an additive free electroless copper so- lution. With the addition of the additives a sig- nificant improvement is observed. The reduction of blistering is attributed to reduced internal stress of the copper deposit. Additives included in the electroless copper so- lution effect the stress of the resulting electro- less copper deposit. Electroless copper deposits normally exhibit compressive stress and tend to lift, or blister, off of smooth surfaces that lack mechanical anchoring sites. With the proper se- lection of additives the stress of the deposit can be significantly reduced. Deposit stress can be measured in a number of ways. A common method in the electroplat- ing industry is through the use of a spiral con- tractometer. The copper deposits of four elec- troless copper solutions containing different additives were evaluated using a Yamamoto JIS- H8626. Figure 4 indicates that internal stress of the deposit is significantly affected by additives. Typical electroless copper solutions utilized in PCB manufacturing are similar to Electroless B A HIGH-RELIABILITY, STRESS-FREE COPPER DEPOSIT FOR FPC, POLYIMIDE AND RIGID-FLEx continues Figure 4: Electroless copper deposit stresses measured by spiral contractometer. additives in the electro- less copper solution have a significant influence on the resulting deposit stress. FeAtuRe