Experience

IEC’s lead-free experience dates back to 1996 when it built the world’s first lead-free telephone assemblies for Nortel.  IEC was awarded an Innovation Citation for that pioneering work (SFX299.pdf ).

Since then, IEC has remained on the forefront of lead-free soldering technology through various development projects completed in its state-of-the-art Materials Analysis Laboratory and through several products built using Pb-Free solder since the introduction of RoHS legislation in 2006.

Extensive process development and analysis activities have been completed using 96.5Sn-3.0Ag-0.5Cu (SAC305) and SN100C solder alloys on a variety of PCB surface finishes.

Microstructural view of SAC305 solder joint from IEC's Materials Analysis Laboratory

Lead-free manufacturing is a mainstream, mature technology at IEC, with thousands of assembled products in the field.  IEC offers all major lead-free soldering processes including reflow soldering, wave soldering, selective soldering and hand soldering.

Understanding

IEC understands the requirements of lead-free soldering and the implications of RoHS-compliance.  All of IEC’s employees have received extensive training covering key aspects of lead-free and RoHS implementation including legislation, effect on industry workmanship standards, soldering materials, manufacturing processes, material identification and reliability.

A dedicated Six Sigma Project Team analyzed the business and manufacturing process flow in 2005 and redesigned or modified those processes to accommodate RoHS-compliance.

The capability of IEC’s equipment set has been verified by building complex test vehicle assemblies and evaluating the reliability of those assemblies.

Frequently Asked Questions (FAQ’s)

What is RoHS?

RoHS refers to a European Union Directive called “Restriction of Hazardous Substances”.  This directive restricts the use of 6 hazardous materials in electronics imported into the EU after July 1, 2006.  The restricted materials are lead (Pb), cadmium, mercury, hexavalent chromium, PBB (polybrominated biphenal) and PDBE (polybrominated diphenal ethers).  Many electronic products are affected, but there are some exemptions.  Refer to the actual directive 2002/95/EC for examples of products that are affected and a list of exemptions.

What material has IEC selected as its preferred lead-free solder alloy?

IEC has selected SAC305 (96.5Sn-3.0Ag-0.5Cu) as its Pb-free solder alloy of choice for reflow soldering operations.  This material melts at 217 °C.

IEC has selected the SN100C alloy for its Pb-free wave soldering and hand-soldering operations.  This tin-copper alloy is compatible with SAC305 and offers many advantages compared to SAC305 for PTH soldering including lower cost, shinier solder joints and lower affinity for dissolving materials such as copper and iron, which preserves solder iron tip life and wave solder machine parts.  The melting temperature for this alloy is 227 °C.

What are my cleaning choices with Pb-free solder?

IEC can support water-soluble or no-clean fluxes for use with Pb-free soldering.

What temperatures do my RoHS-compliant components need to withstand to be compatible with your Pb-free soldering process?

IEC designs its lead-free reflow profile so that the target peak temperature for the coldest solder joint is about 235 °C.  The hotter areas of the board may reach 250 – 260 °C.

Which Pb-free surface finish does IEC recommend for printed circuit boards?

IEC has done all of its development and qualification work using immersion silver and immersion gold (ENIG).

I am converting an existing assembly to RoHS-compliance.  Do I need to change my circuit board material?

IEC recommends that you first check with your PCB fabricator and determine exactly what material is being used and if it meets the chemical definition of RoHS-compliance.  Many fabrication drawings are not very specific, and just specify “FR4 or equivalent”.  If your board material meets the RoHS definition (no banned substances above threshold levels) then it may be possible to keep using the same material.  In general, if you have a relatively simple board (2-6 layers, 0.062 inch, non-challenging via aspect ratios) you may want to build some prototypes to evaluate the existing material before you change.  If you have a moderate to highly complex PCB, or are creating a new design, IEC recommends that you select one of the board materials that were developed specifically for use with a lead-free soldering process.  Ultimately, it is the responsibility of the customer, not IEC, to select the appropriate PCB material for the application.

What is IEC’s policy regarding forward compatibility (using non-compliant parts in a lead-free soldering process)?

IEC contends that there is no forward compatibility and will not use Pb-bearing parts in a Pb-free soldering process.  For one thing, it violates the definition of RoHS-compliance.  From reliability perspective, several studies have shown that small amounts of Pb in a Pb-free solder joint can degrade the reliability.

What is IEC’s policy regarding backward compatibility (using RoHS-compliant parts in a Sn-Pb soldering process)?

In general, most RoHS-compliant parts can be used in a tin-lead soldering process.  IEC’s systems will allow a mix of RoHS-compliant and non-compliant parts to be specified for use on a non-compliant (Sn-Pb) assembly.

There are some exceptions to backward compatibility, however.

IEC does not recommend Pb-free components containing Bismuth for use in a Sn-Pb soldering process.  Sn, Pb and Bi form a low melting temperature alloy that can degrade solder joint reliability.

Area array components such as BGA’s, defined as parts that supply most of the solder for the solder joint, may not be backward compatible.  Pb-free BGA’s with very high melting temperature balls, that will not melt or dissolve during reflow, may be acceptable.  (For example, some ceramic BGA’s use high temperature solder balls that melt above 260 °C.)

Some Customers are concerned about the use of pure Sn finishes due to the potential for tin whisker growth.  If you do not want IEC to use components with pure tin finishes, make sure that your BOM/AVL does not call out any components that contain this finish.  IEC will not deviate from the approved vendor list (AVL) when purchasing components.  If your BOM/AVL does call out components with pure tin finishes, IEC’s systems will allow that component to be used.

I am converting an existing product over to lead-free.  Do I need a new set of assembly tooling?

IEC recommends a new set of assembly tooling for any fixtures, etc. that can come into contact with either solder paste or molten solder.  Stencils and wave solder fixtures are two examples.  The main reason is to prevent cross-contamination of the solder alloys.  Other reasons may include subtle differences in tooling design.
 
I have an existing assembly that I am not converting to lead-free, but one of my BGA’s is now only available Pb-free.  What are my options?

One option is to reball the BGA prior to use.  Remove the lead-free balls and replace them with tin-lead balls.  IEC does offer reballing services, if this approach is selected.

Another option is to reorder the stencil and omit the apertures for the affected BGA.  IEC can screen print the board as normal, then apply tacky flux to the BGA site and place the part.  IEC then uses a “hot” tin-lead profile that ensures that the lead-free BGA balls will melt and collapse.  The net result is that the BGA solder joints will be entirely Pb-free and all of the other solder joints on the board will be tin-lead.

A third option is to attach the Pb-free BGA in a secondary soldering process using a hot-air rework station.

Recent studies have indicated that it may be acceptable to solder BGA’s with SAC-alloy balls using a tin-lead solder paste, as long as the alloys thoroughly mix.  IEC has successfully soldered Pb-free BGA’s using this process, but will not select this approach without customer involvement and consent.

I am converting an existing product to RoHS-compliance.  Are there any design for manufacturability issues that I need to be aware of?

Obviously, you need to make sure that every component on the bill of materials and approved manufacturer list, including the printed circuit board are RoHS-compliant and can withstand the higher temperatures associated with lead-free soldering.

In general, the component land patterns will not need to change to accommodate lead-free soldering.

The self-centering feature associated with tin-lead solders at reflow is weaker with lead-free, so liberal use of local fiducials for BGA’s and QFP’s is recommended so that placement can be dialed in very precisely.

For various reasons, the required use of wave solder should be minimized.  Where possible, design for intrusive reflow, which means that through-hole components should contain stand-off’s and be constructed of high temperature materials.

I need some help converting an existing product over to RoHS-compliance.  Can IEC help?

Yes.  IEC offers a 5-step RoHS conversion process through its Design Engineering Group:

Step 1: Diagnosis Phase (BOM/AVL analysis for RoHS-compliance status)
Step 2: Prognosis Phase (Develop solutions for RoHS exceptions)
Step 3: Treatment Phase (Implement solutions, update documentation)
Step 4: Prototype Phase (Build prototypes)
Step 5: Evaluation Phase (Analyze prototypes in Materials Analysis Lab)

Contact your IEC Program Manager for more details.

How can I get more detail regarding IEC’s RoHS-compliance program or manufacturing processes?

IEC has created a “RoHS Policy Manual” which describes in detail how IEC’s business and manufacturing processes have been designed to ensure RoHS compliance.  Active IEC Customers can request a copy of this policy manual from their Program Manager.