Context: Matte solder is usually fused to provide a better bonding surface or stripped to bare copper. Treatments, such as benzimidazolethiol, prevent surface oxidation of bare copper. The places to which components will be mounted are typically plated, because untreated bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally, any exposed copper was coated with solder by hot air solder levelling (HASL). The HASL finish prevents oxidation from the underlying copper, thereby guaranteeing a solderable surface. This solder was a tin-lead alloy, however new solder compounds are now used to achieve compliance with the RoHS directive in the EU and US, which restricts the use of lead. One of these lead-free compounds is SN100CL, made up of 99.3% tin, 0.7% copper, 0.05% nickel, and a nominal of 60ppm germanium.

Question: What happens to untreated copper that makes it difficult to solder?
Answer: oxidizes

Question: What chemical treatment will prevent bare copper from oxidizing?
Answer: benzimidazolethiol

Question: What's the process by which bare copper gets covered in solder?
Answer: hot air solder levelling

Question: What does hot air solder leveling ensure the coated copper will have?
Answer: solderable surface

Question: What alloy can no longer be used in HASL because of restrictions on the use of one of its metal components?
Answer: tin-lead

Question: Shiny solder is usually fused to do what?
Answer: Unanswerable

Question: What encourages surface oxidation of bare copper?
Answer: Unanswerable

Question: Traditionally, any exposed silver was coated with what?
Answer: Unanswerable

Question: The HASL finish encourages oxidation from what?
Answer: Unanswerable

Question: What is now used in compliance with the RoHS directive in the EU and China?
Answer: Unanswerable