2025) | Complete Questions and Correct
Answers (Verified Answers
/. Affects dimensional stability and changes the electrical characteristic in the material
which can cause potential difficulties in assembly - Answer-Moisture absorption
/.What are the 3 general methods of plating material on PCBs? - Answer-Immersion,
electroless, and electrolytic
/.What are the benefits of metallic coatings / final(surface) finish? - Answer-Corrosion
prevention, Improved long-term solderability
/.Simplest of the wet processes; involves a simple galvanic replacement reaction; the
more noble metal in the solution picks up electrons from the less noble metal immersed
in the solution and plates out - Answer-Immersion Plating
/.Why would you use immersion plating? - Answer-The thickness is limited to a very thin
coating as it is a simple replacement reaction
/.Why is Immersion finishes more beneficial than HASL? - Answer-Immersion has a
flatter base for attachment
/.What are the assembly challenges/problems with HASL process? - Answer-
Coplanarity / solder thickness varies, solder crowning, less uniformity
/.Stencil fits flat on pad, opening is smaller than the land pattern in all dimensions -
Answer-Gasketing
/.What is the problem with gasketing in HASL? - Answer-Uneven surfaces cause
leakage of paste underneath the stencil
/.What other surface finishes are better/flatter than HASL? - Answer-Gray tin,
nickel/gold, nickel/palladium gold, immersion "white" tin, immersion silver, ENIG
/.What surface finish is good for BGAs and surface mount? - Answer-ENIG
/.Why would you use a washable solder mask / what is the advantage? - Answer-
Washable masks are removable; they come off in a cleaning operation
, /.What is plugging? - Answer-Process to ensure that plated through holes are prevent
from being contaminated by the assembly cleaning and plating process chemistries
/.For liquid photo imageable masks, what via process does IPC recommend? - Answer-
Plugging
/.For dry film masks, what via process does IPC recommend? - Answer-Tenting
/.What will manufacturers do to get proper flow characteristics of the prepreg material
and gain better performance of the multilayer structure? - Answer-Manufacturers will
mix and match the various prepreg products
/.For surface mount and for the outer layers to be heat-resistant, what can the
manufacturer do to help this? - Answer-Polyimide material can be used for the outer
layers of a multilayer while inner layers are standard epoxy-grade product
/.In terms of material performance capability, how do you achieve homogenous
construction? - Answer-Same material is used/only slight variations occur between
different material properties. Resin flow of the prepreg must be consistent between the
layers
/.What variation in construction change the physical and electrical performance of pcbs?
- Answer-Differences in overall resin content and the use of different styles of glass
cloth; more resin/glass content can produce the same external thickness
/.Integral part of the manufacturing and testing process; considered in all aspects during
the manufaturing process and NOT confined to an evaluation at the end of the line -
Answer-SPC (Statistical Process Control)
/.What is an example of an SPC? - Answer-In-process coupon evaluation may be cross-
sectioned and evaluated; first article inspection may be performed to ensure the
remainder of the lot would be in conformance
/.These specimens are representative of a the product produced and must represent the
process - Answer-Test coupons / specimens
/.What is the purpose of in-process test coupons? - Answer-Provides a systematic path
for continuous improvement, identifies root causes of problems, reduces the number of
evaluations that need to be made at the end of the production cycle
/.Hole solderability, thermal stress, plating thickness, layer registration, anything related
to hole condition within a 2-sided/multilayer board - Answer-Test coupon AB/R
evaluation
/.Ability of a product to function under given conditions and for a specified period of time
without exceeding acceptable failure limits - Answer-Reliability