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XI. TROUBLESHOOTING SOLDERABILITY
If all variables and parameters which lead to good solderability are not properly
controlled, some typical defects will occur. The description and causes of some
common defects are listed below.
1. Poor Wetting:
Wetting is the primary factor in achieving good solder joints. A condition
when the surfaces to be joined are only partially covered with molten solder,
leaving areas of unwetted surfaces, behind is called non-wetting or poor wetting.
It shows up as pin holes and areas of bare copper or insufficient solder on
the surface of the parts to be soldered. There is virtually no adherence of the
solder.
2. De-wetting:
This condition is similar to poor wetting. It differs in that the areas to which
the solder does not adhere results from the solder pulling back from the
s u r f a c e s prior to solidifying.
3. Disturbed Joint:
When components move in relation to PCB during the solidification stage
disturbed joints are formed.
4. Excess Solder:
This condition occurs when too much solder remains on the joint. Excess
solder joints have solder fillets which appear round and fat.
5. Icicling:
Icicling is excess solder which solidifies during the peel-back stage. An icicle
has a fillet shape which appears conical and ends in a sharp point.
6. Solder Webbing:
When solder adheres to the solder mask between the metallization, it is
called solder webbing. The surface leaves thin lines of solder which form a
pattern resembling a net or web.
7. Pinholes and Blowholes:
Small holes are seen on the solder fillet. The bigger ones are called blow
holes and the smaller ones pinholes. A pinhole often conceals a much larger
internal cavity.
8. Bridging:
