A project manager’s guide to reliability aspects of lead free electronics implementation.
I trust that you are not part of a team that expected to just change the solder from leaded to unleaded and call it good.
If you are part of that team I suggest you start getting the resume up to speed and start browsing Monster: as you have probably got a lot of RMA material heading your way……….8-)
The progject management understanding of quality and reliability benchmarks is fairly critical to the success of any new lead free implementation.
The reason for this is two fold. Firstly the leaded solder used for electronics was originally used for plumbing: in other words it has a long track record of both use in various applications and also in the resulting reliability aspects of the product: if you don’t believe me go take a look in Isaiah 41:7 and e-mail me off line on what you find: ..
Anyhow, suffice it to say that in most cases, we know how to apply leaded solder to form a reliable solder joint, and also know the mechanical characteristics of that solder under subsequent mechanical and thermal stress cycling.
In a lead free assembly the rules are different: most companies take a while to tune in the new process, and the materials have some definitely different mechanical characteristics.
Enter the project management team with checklist in hand and add the following check points:
1 Laminate material thermal stress testing (laminate materials need to withstand higher temperatures to ensure a reliable assembly).
2 Solderable board finish compatibility for lead free.
3 Thermal cycling stress testing (Typically 1000 cycles to a JEDEC spec).
4 Highly Accelerated Life Testing (HALT) (if not already in place) as a part of Design Verification Testing (DVT).
5 Certification of components to have passed Tin Whisker testing (pure tin components can have some extensively documented issues)
6 Drop testing (lead free solder is stronger but more brittle drop testing finds this issue).
7 Component metallurgical compatibility with lead free.
Some of these are checkpoints in project phase 1 but ALL must be complete by FCS (First Customer Shipment) which typically is PLC phase 3. Discuss this with the reliability team. It is really important that the project has gates and checkpoints associated with a lead free soldering system unless this process is already mature and well established in your particular company: in which case you may have relaxed some of the requirements for every product: such as the 1000 cycle thermal testing.
Of course some products require more stringent testing than others. It depends on the equipment lifetime requirements which can vary greatly between equipment types: as an example a mobile telephone has a much lower life expectancy and operating environment that a piece of exchange equipment: so the particular reliability testing model will need to be fine tuned to the product requirement.
And of course in parallel (always!) we have to consider where the product is going to be built: typically at a contract house; which of course will get us another check point when someone from the vendor quality department has been in for an audit – with a RoHS specific audit schedule: ..and so it goes on.
Due diligence is the name of the game in all aspects. Because you “only” changed the solder metallurgy does not mean that you should expect the product to perform identically to the leaded version either in the line yields OR in reliability. In order to achieve this, the engineering and other team members need a true understanding of the issues that may occur and a plan to deal with them and preferably head off any issues before they arise.
Just about all reliability and process issues should have been addressed ahead of the pilot run to allow the pilot yields and subsequent DVT testing to successfully gate the launch of the product into an FCS phase of the project.
In tomorrows blog (Friday) we will be doing a round up of the points to look out for when gating a successful RoHS lead free product implementation and launch.
I hope these few notes are of use, I will be blogging after Friday, but I have to tell you all of this lead free writing this week has given me the appetite to go let some lead fly at a sporting clays range nearby, so the weekend blogs may be being produced later in the day: :
Santa Clara CA, 11/15/07 email john@RoHSUSA.com