Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Cleanliness And Lead Free Conformal Coating Processing


Published on

Conformal coating reliability is a major issue with lead free processing. The factors that influence reliabiltiy include the cleanliness of the board and the proesses used.

Published in: Technology, Business
  • Sex in your area is here: ♥♥♥ ♥♥♥
    Are you sure you want to  Yes  No
    Your message goes here
  • Dating for everyone is here: ❶❶❶ ❶❶❶
    Are you sure you want to  Yes  No
    Your message goes here
  • very good material
    Are you sure you want to  Yes  No
    Your message goes here

Cleanliness And Lead Free Conformal Coating Processing

  1. 1. Lead Free Coating, Cleanliness and the Conformal Coating Process
  2. 2. Outline <ul><li>What is cleanliness? </li></ul><ul><li>Considerations for lead free processing </li></ul><ul><li>Why is cleanliness important for conformal coating? </li></ul><ul><li>How can we measure cleanliness? </li></ul><ul><li>How can we ensure cleanliness? </li></ul>
  3. 3. What is cleanliness? <ul><li>Cleanliness will determine: </li></ul><ul><li>Application performance </li></ul><ul><li>Conformal Coating finish </li></ul><ul><li>Long term circuit reliability </li></ul>
  4. 4. What is Cleanliness? Imagine your bare printed circuit board Plating / Etch Salts Flux Residues Grease / finger salts Oils Soya Sauce
  5. 5. No-clean Flux Residues Grease / finger salts Hand cream Oils (eg. Wave, Silicone ) What is Cleanliness? Imagine your assembled printed circuit board
  6. 6. <ul><li>In a perfect world, substrates would be completely clean before coating </li></ul><ul><li>Can be as many as 13 chemical processes in manufacture </li></ul><ul><li>Interaction between residues? </li></ul>What is Cleanliness?
  7. 7. <ul><li>Different residues have different effects: </li></ul><ul><li>Ionic (flux-residues) – corrosion </li></ul><ul><li>Non-ionic (greases, oils etc.) - coating issues such as de-wetting, delamination </li></ul>Why is Cleanliness Important?
  8. 8. <ul><li>E.g. No Clean flux residues, finger salts </li></ul><ul><li>Osmosis leads to Blistering… leads to Corrosion! </li></ul>The Effect of Ionic Contamination
  9. 9. <ul><li>What is Osmosis? </li></ul><ul><li>“ pumping action” caused by: </li></ul><ul><li>a contaminant solubalising and re-crystallising between the coating film and substrate, as moist air moves in and out. </li></ul><ul><li>The contaminant is usually a salt and each induces different osmotic pressure which may be extreme. </li></ul>Conformal Coating
  10. 10. Contaminant left on a coated board at 25 o C 50% RH
  11. 11. Board exposed to Humidity
  12. 12. Moisture has “found” contaminant, and a blister has formed through osmotic pressure
  13. 13. The soluble contaminate has now formed a conductive fluid with the moisture
  14. 14. A dendrite is forming between tracks
  15. 15. <ul><li>Dendrites are a problem! </li></ul><ul><li>Grow and blow phenomenon </li></ul><ul><li>Estimated root cause of 25% of returns </li></ul>Conformal Coating
  16. 16. Corrosion On Pin Delamination Of Coating Coating Dissolving & Cracking In Circled Area
  17. 17. Non-ionic contamination <ul><li>Major Problems seen during conformal coating application: </li></ul><ul><li>Conformal Coating de-wetting </li></ul><ul><li>Lack of adhesion of conformal coating </li></ul><ul><li>Delamination of conformal coating </li></ul>
  18. 18. Where do residues come from? <ul><li>Board fabrication </li></ul><ul><li>Components </li></ul><ul><li>Assembly equipment </li></ul><ul><li>Soldering processes </li></ul><ul><li>Operator handling </li></ul><ul><li>Incorrect cleaning </li></ul>
  19. 19. So you’re told to use no clean <ul><li>In the past to produce Hi-Reliability boards without cleaning would not have been considered. It can be now, if :- </li></ul><ul><li>Incoming boards and components inspected for cleanliness. </li></ul><ul><li>All operators doing in-process handling should wear gloves. </li></ul><ul><li>“ low residue” no clean flux/paste is used. </li></ul>
  20. 20. So you’re told to use no clean <ul><li>The soldering window must be fine tuned and the system controlled. </li></ul><ul><li>Low residue wire/flux used for rework. </li></ul><ul><li>Process controls are put in place. </li></ul><ul><li>The process is validated. </li></ul>
  21. 21. SMT with lead free solders <ul><li>Key variables summary </li></ul><ul><li>Melting temperature of alloy </li></ul><ul><li>Flux chemistry - activation, temperature effects </li></ul><ul><li>Wetting and surface tension properties of the alloy </li></ul><ul><li>Solder balling and bridging potential increases </li></ul><ul><li>Component / board reliability </li></ul><ul><li>Compatible rework / repair </li></ul><ul><li>Compatible wave, selective soldering process </li></ul>
  22. 22. Compare SnPb and SnAgCu <ul><li>Tin-Lead 183°C </li></ul><ul><li>Tin-Silver-Copper 217°- 220 ° C </li></ul>
  23. 23. New Solder Paste chemistries <ul><li>New activators </li></ul><ul><li>New resins </li></ul><ul><li>New gelling agents </li></ul><ul><li>Better surfactants </li></ul><ul><li>Additives to prevent oxidation </li></ul><ul><li>Alloy specific fluxes </li></ul><ul><li>Give rheological character </li></ul><ul><li>Aid stencil release </li></ul><ul><li>Hold components prior to reflow </li></ul><ul><li>Remove oxides from the surfaces to be joined </li></ul><ul><li>Protect against further oxidation </li></ul><ul><li>Reduce surface tension in the soldering process </li></ul>
  24. 24. Lead free and Tin Whiskers <ul><li>What are they ? </li></ul><ul><li>Single crystal grow from electroplated tin coatings. </li></ul><ul><li>Needle like, spiral, modules, mounds </li></ul><ul><li>Diameter approximately 3-5um </li></ul><ul><li>Various lengths, shape from micrometer up to mm’s </li></ul><ul><li>A form of metallurgical stress release </li></ul>
  25. 25. SEM Photograph 150 and 900 magnification, 3 months aging Tin Whisker on Pure SnPb
  26. 26. Sn Plated Chip Caps
  27. 27. Lead free and Dendrites <ul><li>High Sn & Ag alloys promote dendritic growth </li></ul>
  28. 28. Lead free and Dendrites <ul><li>Field Failure due to dendritic growth </li></ul>
  29. 29. Summary Lead free and Reliability <ul><li>High Sn & Ag alloys are prone to dendritic and tin whisker growth. </li></ul><ul><li>Conformal coating reduces the problem. </li></ul><ul><li>All lead free fluxes are higher activation than Pb alloy solders. </li></ul><ul><li>Higher flux residue volumes. </li></ul><ul><li>Lead free & VOC free wave solder flux is 3 x solids content. </li></ul><ul><li>Less compatible than leaded solder residues. </li></ul><ul><li>More requirement to test compatibility. </li></ul><ul><li>UV40 adds mechanical stability to lead free alloys and is our hardest coating. </li></ul>
  30. 30. Further Information <ul><li>Website </li></ul><ul><li> </li></ul><ul><li>FAQs </li></ul><ul><li> </li></ul><ul><li>Technical Documents and bulletins </li></ul><ul><li> </li></ul>