TY  - JOUR
AB  - The industry trend towards higher density interconnect
on PWBs has caused board fabricators to explore alternatives to the traditional hot air solder
levelling (HASL) technology. Problems with pad planarity in the assembly of fine
pitch devices with high I/O counts are well documented. Organic finishes based on
substituted imidazoles address some of the assembly requirements, as do precious metal finishes
such as gold and palladium. However, both types of solderable finish have limitations or
undesirable characteristics. This paper discusses and compares other
non‐precious metal systems as alternative solderable finishes. Immersion plating
processes based upon bismuth and silver have been developed, and the data presented
demonstrate that the solderability of these systems is superior to that of organic and palladium
finishes. Test results on hole‐fill, solder‐spread and meniscograph
(wetting balance) are extensively discussed in this study. Potential concerns over joint
reliability and diffusion are addressed. The chemistry of these non‐precious
metal systems also affords benefits to the PWB fabricator. These include increased yields,
reduced costs and the elimination of soldermask compatibility issues. Considering
possible future industry trends, a significant advantage of these materials is their full
compatibility with lead‐free solders. Data on compatibility with solder replacements and
wire‐bonding technology are also presented.
VL  - 23
IS  - 2
SN  - 0305-6120
DO  - 10.1108/03056129710370178
UR  - https://doi.org/10.1108/03056129710370178
AU  - McGrath P.
AU  - Soutar A.
PY  - 1997
Y1  - 1997/01/01
TI  - Non‐precious Metal Finishes for Fine Pitch Assembly
T2  - Circuit World
PB  - MCB UP Ltd
SP  - 42
EP  - 45
Y2  - 2024/04/26
ER  -