Context: The hole walls for boards with two or more layers can be made conductive and then electroplated with copper to form plated-through holes.  These holes electrically connect the conducting layers of the PCB. For multi-layer boards, those with three layers or more, drilling typically produces a smear of the high temperature decomposition products of bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process, or by plasma-etch. The de-smear process ensures that a good connection is made to the copper layers when the hole is plated through. On high reliability boards a process called etch-back is performed chemically with a potassium permanganate based etchant or plasma. The etch-back removes resin and the glass fibers so that the copper layers extend into the hole and as the hole is plated become integral with the deposited copper.

Question: What do the hole walls in two-layer PCBs have to be before they can be electroplated?
Answer: conductive

Question: What's the minimum number of layers a PCB can have to be considered "multi-layer"?
Answer: three

Question: What process does a multi-layer PCB usually undergo before plating to make sure the layers have good connectivity with each other?
Answer: de-smear

Question: What type of boards undergo the etch-back process?
Answer: high reliability

Question: Etch-back removes glass fibers and what other material?
Answer: resin

Question: What connects the conducting layers of the PAB?
Answer: Unanswerable

Question: Smears are removed with a chemical smear what?
Answer: Unanswerable

Question: The process used on low-reliability boards is called what?
Answer: Unanswerable

Question: The back-etch removes what?
Answer: Unanswerable

Question: What becomes integral with the deposited silver?
Answer: Unanswerable