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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)





PRINTED CIRCUIT BOARDS

1 . I want to change the printed board finish on my PCBs what options do I have for lead-free?
2 . If I have lead-free flexible circuit to assemble, how can I hold them flat during reflow?
3 . Many people tell me I have to change the laminate material I use for my designs when I move to lead-free is this the case?
4 . My printed boards are not supplied flat, many of the circuits I receive are like bananas and give me problems during solder paste printing and component placement can you help.
5 . Solderability testing is a problem for us with surface mount boards. How can we test boards and get a direct measurement on surface mount pads down to 0.025".
6 . What are the main problems with copper OSP finish boards?

 

I want to change the printed board finish on my PCBs what options do I have for lead-free?
To answer this question could take a long time, simply in terms of solderability, solder levelled Lead-free, gold over nickel, silver, tin and then copper OSP. Each has its advantages and disadvantages but find out what you supplier currently has available. See the results of my lead-free trials on each of the different solder finishes in the Lead Free Experience Report available from the LEADOUT web site.

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If I have lead-free flexible circuit to assemble, how can I hold them flat during reflow?
Yes this is a nice one, as we increase convection rates during reflow the flexibles tend to flap, moving components out of position. Recently I have just run a line with flex circuits with some success with tin/silver/copper paste. Depending on volumes the best way is to hold the circuits flat on jigs/pallets. A two part laminate jig can sandwich the flexible, solder paste is dispensed at high speed, components placed and then reflowed. Using a cover plate over the flexible as part of a two piece jig prevents screen printing from being used.
Basically this time I used a pallet with sprung mounted clips in the four corners of the pallet, this then passed through print, placement, reflow and automatic inspection with little problem.

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Many people tell me I have to change the laminate material I use for my designs when I move to lead-free is this the case?
In most cases no, there are benefits but in most cases its not necessary.

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My printed boards are not supplied flat, many of the circuits I receive are like bananas and give me problems during solder paste printing and component placement can you help.
Sorry, but this is a common problem, the current European specifications at its maximum limit for flatness are not suitable for production. The component assembly equipment manufacturers are now specifying tolerances tighter than the specification you will have to specify what your pick and place manufacturer recommends.
A guide of flatness and some of the problems is available as a draft guide from BSI unfortunately its not a specification. Two causes of action are open to you. Give your supplier a customer detailed specification which is tighter than the national spec. Alternatively specify a laminate which has a better specification and review the process being specified for the manufacture of the board. Examine your board design, is it of a balanced construction.
It may be surprising to may people but so far I have not experienced any issues of flatness problems with lead-free, perhaps this is yet to come.

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Solderability testing is a problem for us with surface mount boards. How can we test boards and get a direct measurement on surface mount pads down to 0.025".
Solderability testing of surface mount pads is a problem using the old methods contained in existing European specifications. The only way of getting repeatable results is by using a wetting balance. All PCB manufacturers will have to consider testing boards in the future to far higher standards.
Equipment is available where the actual wetting force is measured by the equipment on individual surface mount pads. NPL use this technique on all their lead-free studies. A sample test board is produced with a minimum of five pads. The sample is fluxed and suspended at 45o to a solder globule. The board sample is prepared so that the line of pads is on the edge of the sample.
The sample after fluxing is brought into contact with the globule of solder. By mounting the sample at 45o it makes sure the pad surface is allowed to wet rather than the substrate material affecting the buoyancy of the sample. Visit the NPL web site and have a look at their results: www.npl.co.uk/ei.

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What are the main problems with copper OSP finish boards?
Despite the literature from the protective finish manufacturers heat does effect the copper circuit. It increases the time to obtain full wetting hence increasing the possibility of poor yield. Double sided reflow again increases the surface oxides and poor yield. You need to confirm the quality of the basic coating with your supplier and consider the other process stages which effect solderability. Cleaning the board, washing off poor paste prints, poor board handling, the original surface preparation of the copper before treatment all can effect soldering yields if not done correctly.

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