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 FAQ's

  . COMPONENTS (8 questions)
  . HAND SOLDERING AND DE-SOLDERING (3 questions)
  . INSPECTION (3 questions)
  . PRINTED BOARD DESIGN (3 questions)
  . PRINTED CIRCUIT BOARDS (6 questions)
  . REFLOW SOLDERING (5 questions)
  . REWORK (1 questions)
  . SCREEN PRINTING (2 questions)
  . WAVE SOLDERING (4 questions)
  . X-RAY INSPECTION (1 questions)





COMPONENTS

1 . Are there any good books covering lead-free manufacture?
2 . Does chip capacitor cracking occur more in wave soldering or reflow soldering?
3 . I have a large stock of tin/lead coated component terminations can I use these with lead-free solder to use up the stock?
4 . I have been having a problem with cracked Ball Grid Array devices, is this common?
5 . I have seen Quad Flat Packages in special sealed foil packaging from the supplier should this be opened at goods receipt?
6 . We are not sure if surface mount is right for our company our products we do not need miniaturisation. Now we have to move to lead-free manufacture, should we convert our products?
7 . What shelf life should we expect in terms of solderability of surface mount component terminations?
8 . With lead-free what are the typical temperatures that components have to withstand?

 

Are there any good books covering lead-free manufacture?
Surprisingly there are quite a few books published and some reviews are available at LEADOUT and SMART Group websites.

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Does chip capacitor cracking occur more in wave soldering or reflow soldering?
Cracking of components today is mostly seen due to flexture failure after soldering not due to the soldering process. It did use to be the case many years ago that components were seen to fail after wave soldering. In many cases they had already been damaged by the placement systems. If this is the case today it is more likely to be a quality problem with the components. In lead-free soldering temperature rise but the problem is more likely to be associated by board flex.
As further points just check you specify capacitors with a nickel barrier layer on your terminations. It should be standard practice but I have seen a few examples of solder leaching with lead-free.

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I have a large stock of tin/lead coated component terminations can I use these with lead-free solder to use up the stock?
First if you use components or terminations that are plated or dip coated with tin/lead the product produced will not be RoHS compliant.
If small amounts of lead are present at the component termination interface in a lead-free alloy joint they can create a low melting point phase in the joint. This can be separated from the bulk of the solder joint previously produced in a reflow joint at a much lower temperature than the main joint. Some people refer to this as a hot tear or a soft fracture which can happen as the joint reaches normal soldering temperatures for tin/lead like 180degC.
Basically as the board goes through the next process if the joints reach this temperature the leads can separate from the joint. This has mainly been seen in manufacture when boards are passed over the wave soldering system and the top side of the board is too hot. There are a number of cases of this happening on products from Japan as they were very early to produce lead-free products. It can also happen in other processes during assembly.
Recent project work with the National Physical Laboratory NPL in a Lead-Free Transition Studio Project has demonstrated that solder joints that are produced with lead contamination, where a full mix of the tin/lead and lead-free alloy like SnAgCu occurs the joints are reliable through many thermal cycles and vibration. Reports available at www.npl.co.uk/ei.
At present lead contamination is a legislation issue and can also be an assembly issue.

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I have been having a problem with cracked Ball Grid Array devices, is this common?
BGA cracking or Popcorning can occur on plastic parts and is normally seen at the plastic to fibre glass substrate interface. This is the weakest junction and if any moisture is present in the parts during reflow or rework it expands and escapes at the side. Normally either the internal bond wires are broken or the die lifts. If you have it today with tin/lead it will be worse with lead-free and you need to improve your handling procedures!

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I have seen Quad Flat Packages in special sealed foil packaging from the supplier should this be opened at goods receipt?
Avoid opening the packaging until you need to assemble devices the supplier will specify any special handing. It is an attempt to prevent cracking of the devices during reflow or rework assembly. If large plastic parts QFPs are received and the packaging is open send them back. If you accept them you are accepting the responsibility for processing the parts and any failures the supplier/distributor will not accept the problem.

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We are not sure if surface mount is right for our company our products we do not need miniaturisation. Now we have to move to lead-free manufacture, should we convert our products?
If you don't need SMT then don't use it. But be aware that over 85% of products world wide use SMT. Many of the new components are only available in this format. If you are not sure then arrange for a training course for your design, production and management team. Understand the benefits and disadvantages and review designs and costs, obtain an independent opinion. Using surface mount and reflow is much easier to implement in lead-free manufacture.

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What shelf life should we expect in terms of solderability of surface mount component terminations?
All components should be solderable after one year after purchase from your supplier regardless if the supplier is a distributor or the original manufacturer. Normally any reputable supplier will guarantee the solderability life of parts for that period in normal storage conditions. If not, change the supplier. Experience shows that the finishes being used for lead-free terminations well exceed this and the solderability should not be a major issue. You are more likely to get parts that are poor when you receive them.

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With lead-free what are the typical temperatures that components have to withstand?
Specifications for testing parts exist from IPC and JEDEC but to answer the question here are some typical temperatures for soldering lead-free. Wave soldering 260oC, convection reflow 240oC, Vapour Phase reflow 230oC and rework 230-250oC.

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