1107 Electronic Definition or Meaning for lead free solder

Definition for lead free solder


What do you think what is lead free solder?
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was Sn Pb tin lead proposal for lead free is Sn Ag Cu tin silver copper

1. Get up-to-date with the proposed EC directive
Although there is no current legislation enforcing the use of lead-free manufacturing, there is a proposed European Union Waste in Electronics and Electrical Equipment (WEEE) Directive that could ban the use of lead entirely from European electronics assembly processes and boards by 2004. Most observers now feel that its adoption in some form or other will be inevitable sooner or later.
It is therefore vital to get a copy of the latest (2nd) draft of this directive and keep completely up-to-date with all subsequent developments. The environmentally driven legistation will also have major implications for both the design and recycling of boards and products. This is because eliminating lead in electronics manufacturing is only one of a number of wide ranging directives that are proposed in the WEEE document.
The legislation, for example, would also place stringent controls on products containing lead and other environmentally hazardous materials, such as mercury, asbestos and haloggenated-flame retardants.

2. Consider switching to lead-free components now.
One common source of lead that is more straightforward to eliminate from your boards is contained within component terminations. This is a good place to begin any serious commitment to eventually switching to lead- free and doesn`t carry a cost penalty.
Bearing in mind that component stocks can be kept in a factory for some time, it would be a good idea to carry out an inventory to establish what proportion of stock has lead-based termi- nations. Do not continue stocking up on long shelf life components that may become unsuitable or unus- able in a lead-free process.
It would also be a good idea to inform suppliers of your possible intention to go lead-free in order to check out their lead-free policy and capabilities. If they do not have a positive policy for supplying lead-free compo- nents in the near future you may need to start looking for an alternative supplier.

3. Consider switching to lead-free boards .Similarly, it would make good sense to approach your existing bare board suppliers to ensure that they will be able to supply you with lead- free PCB finishes that won`t contaminate lead-free solder joints and solder pots.
By performing these first three steps alone, you will already be way ahead of most manufacturers in switching to lead-free manufacturing. This could create some welcome breathing space if (or when) the draft legislation becomes manda- tory.

4. Decide which lead-free solder alloy you
are going to use.
It is at this stage that diffi- culties can begin to arise, this would be a good time to set up a small lead-free working group to investi- gate the major implications of switching to a totally lead-free manufacturing process. It is also a good time to involve your current solder supplier and lean on
its expertise. Because lead-free processes can be degraded by lead contamination from other sources, a switch to lead-free has to be total. This will obviously involve replacing all existing lead- based cored wire, flow-sol- der baths and surface mount solder creams with suitable lead-free alternatives. Care should be taken to include re-work, repair and off-site soldering.
There is, however no drop-in replacement. For electronics assembly, the conventional tin-lead solder alloy (Sn6O, Pb4O) has a list of attributes that make pro- ducing an exact replacement almost impossible. Its tem- perature range, condijctivi- ty, cost, availability, re- work characteristics, mechanical strength, non-aggressive fluxes, low tool cost, long life, ease-of- use and ability to join a wide variety of metals and alloys make it a hard act to follow.
All Almit`s research to date has indicated that any lead-free or low lead solder will almost certainly be a tin based alloy, and that there is a shortage of suitable alloy- ing elements with which to create a suitable solder material (price, availability, toxicity etc)
There are, however, a vast number of different lead-free solder alloys from which to choose. Tin-cop- per-silver (Sn,Cu,Ag) cur- rently seems to be the most popular choice for cored wire and surface mount applications, with tin-copper (Sn,Cu) for wave soldering.
Ironically, this mirrors existing practices. Very few manufacturers use silver in their flow solder baths due to its cost and the fact that it drosses off quickly. Instead they opt for a straight tin- lead alloy (Sn, Pb) and restrict the use of tin-lead- silver to hand soldering and surface mount applications.
Having chosen your basic alloy, there are further refinements that can be made. To enhance solder- ing characteristics small (two to four per cent ) addi- tions of other metals can be made. Bismuth, for exam- ple can be added to lower melting temperatures, but other alternatives include indium and antimony each of which will have different physical and mechanical effects on an alloy`s perfor- mance.
Smaller companies that do not have the necessary research facilities should follow the lead of larger manufacturers in selecting a suitable lead-free solder alloy, and of course seek the advice of their solder sup- pliers.
Lead-free fluxes will be pretty much the same as current fluxes. This means that the performance of any lead-free solder will rely to a greater or lesser extent on the performance of its flux. Manufacturers may wish t
try a variety of solders from different vendors. There is a wide choice of lead-free and low-lead solders cur- rently available from estab- lished suppliers.

5. Look at your assembly processes and procedures.
Lead-free solders will demand some significant process changes. The lead free process temperatures is in general around 30 to 40`C higher than those of conventional lead based solders. Problems here are with board materials and components.
Manufacturers will need to take a close took at their reflow ovens and wave soldering machines to make sure that they are capable of handling the increased process temperatures and can maintain the tighter temperature control requirements demanded by lead-free solder materials.
This also means it may not be sensible to buy any new process equipment unless it is capable of handling substantially higher process temperatures. You may run the risk of investing thousands of pounds in machinery that could become redundant within a few years if the lead free legislation is adopted.
Manufacturers will also have to establish some very strict in-house quality and process controls to ensure that all the leaded solder is disposed of as they move over to a lead-free process.
This will create a tremen- dous logistics and quality control challenge to continu- ally separate and identify lead-free and lead-based sol- der pastes, bars and wire. They will all look physically identical.

6. Set up some pilot trials.
Having identified a suitable lead-free alloy and tailored your production process machinery accordingly, it is now time to start doing some serious pre-production trials.
This should ideally begin with pilot schemes and eventually move onto full production builds long before the anticipated legis- lation makes this mandatory.

7. Greener design for manufacture.
Another important area of the proposed directive that manufacturers will need to address involves the actual design and layout of the boards and products.
According to the WEEE documentation, all boards and products will have to be designed to be suitable for recycling and up-grading.
In terms of recycling, this means that product parts including the PCBS, need to be designed for ease of disman- tling and all materials used should be easily identifiable.
Clipping and screwing will therefore be preferred to welding, so that when a product reaches the end of its life it can be easily and quickly broken down into recy- clable compo- nent parts. These will no doubt be thrown into separate materi- al bins in a recycling pro-
duction line. To this extent, all plastic components weighing over 25g will need to be marked with some material identification.
The logic behind the up- grading stipulation is that when a current generation of products goes from one ver- sion to the next, they should be easily upgradeable. This is an effort to reduce the vol- umes of electrical waste pro- duced by allowing customers to easily up-grade products rather than throw them away and buy new ones.

8. You will be responsible for re-cycling your own products.
Article 5 of the proposed directive would make man- ufacturers entirely respon- sible for recycling all equipment they produce free-of-charge to the end user.
So (in theory) the owner of an old TV will be able to send it back to the manufacturer who, by law, will be responsible for recycling it. This creates major logistics problems which companies should be building into their long term business plans in order to make this either a non-cost, or better still, a profitable exercise.

9. Consider the rework and repair implications.
If you`re producing a prod- uct that is exported around the world, it may not be that easy to carry out rework on a product built with lead- free solder. The board will have to be marked in some fashion to indicate the alloy used to enable rework to be carried out by loca4 service and support engineers. At the moment you are virtual- ly safe to assume solder is a tin-lead alloy, but that assumption will not be able to be made in the future.
While lead solder may become illegal in 2004, mil- lions of electronics products on the market have lead sol- der in them and will need to be repaired with lead solder for many years to come. So lead-based solders will have to be produced to enable repairs to be carried out. It is also vital that safeguards be put in place to avoid lead-free solders being repaired with incompatible lead-based materials. This could make field repair dif- ficult or even dangerous (from a reliability point of view).

10. Consider sub-contract implications.
If you make heavy use of sub-contractors then you will have to liaise closely with them about your lead- free needs. They may also be under pressure from cus- tomers to use several differ- ent lead-free alloys, which could prove almost impossi- ble. So be prepared for the response. `This is the lead- free-alloy we use, take it or leave it`.

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