A HASL SUB-CONTRACT SERVICE SYNONYMOUS WITH QUALITY
None of the 'non fused' surface protective coatings can guarantee solderability. Some 'alternative' coatings that have proven reliability when using lead solder may be less reliable at the higher time/temperature cycles demanded by lead free assembly.
Spread and fillet angle
Lead Free Solder paste will not spread beyond the printed area with most protective coatings. HASL pre wetted surfaces however ensure complete coverage to the periphery of the pad.
Cost and Reliability
HASL has always been the ultimate QA tool. The process highlights material and manufacturing defects on the bare board, as received, prior to assembly.
Demand for LEAD FREE HASL continues to increase as more and more assemblers recognise the advantage of assembling onto solder rather than a 'protected' copper surface.
Free of Charge lead free soldering trials are available, contact Cemco Services for information.
Q. Can you remove Conventional SnPb HASL and replace it with Lead Free?
YES but only after chemical stripping. The proposed upper limit for lead in lead free solder is 0.1% by weight. Reprocessing circuits would rapidly contaminate the solder pot.
Q. Will LEAD FREE solder provide a more planar surface?
YES. Our experience has shown that large surface areas (always the thinnest coating) are between 40% and 80% thicker and small areas (always the thickest coating) are between 40% and 80% thinner.
Q. Will holes clear?
YES. Hole clearing is better with lead free solders.
Q. Won’t LF HASL leach too much copper?
NO. All protective coatings demand micro etching prior to application. HASL generally requires less as the process confirms solderability. Electroless metal deposition is a conversion process, replacing copper 1-1 with Tin or Silver.
All soldering operations will dissolve copper proportional to time and temperature. Some alloys dissolve copper faster than others. In our experience the 3-4%Ag SAC alloys are the worst, dissolving approximately 1 micron after a six-second immersion at 275 C. The Ni stabilised SnCu alloys seem to be the best at around 0.5 Microns. Horizontal leveling results in a contact time of approximately 2 seconds, Vertical Leveling approximately 5 Seconds.
We have conducted controlled dissolution testing with 6 different alloys including SnPb. Results are available to interested parties.
Q. Won't the higher temperatures result in too much thermal shock or Z-axis expansion damage?
We have processed all types of circuit from phenolic paper to 6mm thick backplanes over the past 7 years and have had no reported damage or degradation resulting from the higher time temperature cycles used.
BUT HASL DOESN'T MEET MY ASSEMBLY PROCESS REQUIREMENTS…
Is it HASL that doesn't meet you requirements or is it the HASL quality you have experienced? Why not send us samples of you most problematic boards and see what can be done or visit by appointment or one of our open days.
IMMERSION SILVER FINISHING SUB-CONTRACT SERVICE
Cemco Services are now offering a new sub-contract Immersion Silver Finishing service. As always you can be assured that you will receive a high standard of service and quality you have come to expect from the Cemco Services HASL process and as with all our processes, we will be happy to process samples FOC for you to inspect and test.
For further details, questions or to book your boards in, please contact Chipi on 02392 241166 / 02392 246023 or firstname.lastname@example.org
If you have a requirement for any other 'alternative' surface finish or other out-source service, please contact us as we would be happy to install additional equipment or processes should there be sufficient interest.
CEMCO SERVICES LTD
1-2 Silverthorne Way
Hants PO7 7XB
Tel: + 44 (0)23 9224 1166
Fax: + 44 (0)23 9226 2089
Contact: Paula Partridge
QUICKSILVER SERVICES LTD