Three years ago a survey was conducted by the SMART Group of 250 printed board
suppliers on their current and preferred solderable finish for surface mount
boards. The 1993 results and the latest 1996 results are included here for your
reference.

The manufacturers were first asked which solderable finishes do they currently
offer their customers for surface mount products. The most widely offered finish
was solder levelled (24%) with traditional tin/lead reflow (22%). Gold over
nickel was offered by 17% of the companies. Other finishes which were offered
for surface mount boards were immersion tin, roller tin, nickel, horizontal
levelling, bare copper with no protective coating and solder paste and reflow.
Only one or two companies offered any of these alternatives. Two of the
suppliers offering these alternatives were involved in flexible circuit
manufacturer.  

The printed board manufacturers who responded indicated that in terms of volume
of boards or square inches solder levelling was the most often specified finish
(69%) followed by traditional tin/lead finish (26%) and organic coatings (5%).
The solder levelling process was indicated by 52% of the companies as offering
the best compromise between the requirements of the assembler and the ease of
fabrication. There was very little difference between the three other finishes
tin/lead reflow, gold over nickel or organic coatings.

In terms of popularity with customers the following finishes are being  most
often requested for surface mount products. The finishes are listed in order of
popularity. 1. Solder Levelling, 2. Tin/Lead Reflow, 3. Gold over Nickel, 4.
Brushed Tin/Lead, 5. Organic Coating (Entek, Glicoat T), 6. Flux Lacquer Coating
(Different Manufacturers)

The costs below were based on the cost model on the survey. Copper protective
finish 500 PCB's L8.84 each 1000 PCB's L8.28 each - Hot air levelled 500 PCB's
L9.44 each 1000 PCB's L8.85 each -Nickel/gold 500 PCB's L9.51 each 1000 PCB's
L8.95 each.  The one off tooling costs were L426 Electrical test fixturing L550

The model printed board for cost calculation is a double sided board produced
from FR4 laminate incorporating surface mount pads down to 0.025" pitch on both
sides. The board size is 6.28" x 8.95" with photoimagable solder resist on both
sides and silk screen legend on one side. There are 2368 holes, four different
sizes the smallest being 0.018". Track size is 0.006" with 0.008" spaces. An
estimate of 20% should be used for open copper areas requiring the solderable
finish. The price should be shown for a single batch of 500 and a 1000 boards
with the tooling costs.

The latest survey results (May 96) are currently based on 22 respondents showed
the most widely offered finish was solder levelled (55%) with traditional
tin/lead reflow (15%). Gold over nickel was offered by (20%) of the companies.

The printed board manufacturers who responded indicated that in terms of volume
of boards or square inches solder levelling was the most often specified finish
(72%) followed by traditional tin/lead finish (10%) Gold (10%) and organic
coatings OSP (8%). The solder levelling process was indicated by 90% of the
companies as offering the best compromise between the requirements of the
assembler and the ease of fabrication. In terms of popularity with customers the
following finishes are being  most often requested for surface mount products.
The finishes are listed in order of popularity. 
1. Solder Levelling , 2. Nickel Gold , 3. Copper OSP , 4. Tin Lead Reflow , 5.
Silver .

The following are the average cost quoted based on the model. Copper protective
OSP finish 500 items L7.60 1000 items L6.99, Hot air levelled 500 items L9.77
1000 items L8.85 , Nickel/gold 500 items L9.82 1000 items L9.42 Other finish
Silver 500 items L8.75 1000 items L8.55 Tooling cost L127 Electrical test
fixturing L379


Bob Willis
SMART Group
Europes Largest Surface Mount Technology Association