Hi Richard
Could not agree more with Ed ; = feel guilty & out of time .
What I can tell you as we go through TH > SM conversion right now on the
overall process you save 15-20% , that is materials, directs, OHs , etc.
I did very detailed study for cost benefits validations, inclusive the
subcontract options ( TH inhouse x SM inhouse x SM contract ) .
I think you go through the same .
Let me know if that is so, I'll try to generalise my ( confidential )
spreadsheet over Holidays for outside use .
Let me know the fax No. too , I have some old papers and no scanner .
See you [www.resmed.com] Paul
>----------
>From: Ed Holton[SMTP:[log in to unmask]]
>Sent: Wednesday, December 24, 1997 6:14 AM
>To: [log in to unmask]
>Subject: Re: [TN] Cost comparisons TH vs SMT
>
>Richard
>
>I understand your frustration about having your question not answered, as
>it has also happened to me in the past. But don't give up the fight, you
>should be applauded for asking the question. That is a much better
>attitude then never asking. . .
>
>I do not have any hard numbers for you about thru-hole vs SMT components,
>but your design should not be based just on component cost alone. There
>are numerous intangibles that must be considered:
>
>Placement: SMT has the capability of 6 sigma quality for placement while
>TH is approximately 3 sigma. For example, most TH machines will have 3
>mis-insertions out of a thousand. SMT is significantly better. You need
>to consider the quality improvements of SMT over TH and the increased
>efficiency.
>
>Optimization of process. Design your board for all SMT and you only need a
>SMT line. Add in TH and now you need TH machines and a wave solder.
>
>Efficiency/speed: I have yet to see a TH machine reach 40K plus placements
>an hour.
>
>Soldering: SMT reflow is capable of higher quality levels than wave
>soldering (however I must brag that I am below 100 ppm with my wave solder
>process! Thank you to Bob Willis, Ray Rua, John Maxwell and SEHO who have
>helped me achieve this)
>
>In my opinion, it is better to spend a few more cents for all SMT and
>increase first time yields and throughput rather than some of the known
>fallout due to TH and wave soldering. However, keep reading because there
>are many more caveats to consider. (I work in automotive electronics where
>every cent counts, however I firmly believe that spending more on the
>components will save on rework/repair cost. These are hidden costs, that
>the customer never sees except when accounting calculates the overhead.
>Have gone many rounds on this with accounting)
>
>Component cost. Many SMD components are cheaper than TH, especially chip
>capacitors and resistors. But there are many high voltage devices and
>connectors that are still less expensive as TH. However, I have seen the
>cost of many components drop such that when the program was first
>developed, TH was cheaper, but within 3 years, the SM components were a
>better deal. Consider the future of components when designing.
>
>DIP components. While a DIP package may be more cost effective than an
>SOIC, the placement issues between the two of them, plus the need for a DIP
>inserter as a special piece of equipment vs. the SMD placement machines
>that place chips to quads, we eliminated all DIP components from future
>designs.
>
>Look at commonization of components to get better volume discounts, what
>components are used in design today at your facility?
>
>Optimization of process: Some components are not available in SMT packages
>and you are forced to use TH. If this is the case, consider using more of
>the same kind of TH components to efficiently use the TH machine (this
>usually happens with radial components) and balance the process time
>between the two machines.
>
>The list goes on and on. Basically, don't decide the design just on the
>cost of the components, you will get burned and your M.E.'s will hate you
>(haha). Many other factors should drive the decision. At a previous
>employer, i started to develop design guide lines based on the
>manufacturing capability of the production floor. As a designer, you
>should know what your capabilities are, and what the ME group has planned
>in the future.
>
>Here is a sample for you. I proposed to our designers/engineers when
>designing a new board:
>1. make it all top side SMT. (one process and you are done)
>2. make it top side SMT with thru-hole soldered using paste in hole
>technique. (new process development)
>3. make it top and bottom SMT reflow (same amount of equipment required as
>in number 1, but double the assembly time)
>
>Here is where it gets tricky:
>if significant TH is required you have three options:
>4A. reflow SMD, insert TH and wave solder or selective solder the TH
>joints
>4B. Adhesive attach SMD to bottomside (including SOIC's and Quads), insert
>TH and wave solder the whole thing (but your wave solder better be in
>control, pad design, etc.)(This might allow use of CEM1 as opposed to FR4,
>what a cost savings!!)
>
>5. topside reflow, TH, bottomside adhesive and wave solder the whole thing
>(yes, these are all variations on type I, II, and III)
>
>BUT, after all the above have been considered, the whole group needs to
>discuss the best design, based on efficiency, quality, through-put,
>component cost, etc.
>
>So, I hope this sheds some light on your issue. No hard numbers, but some
>other things to consider.
>
>Ed Holton
>Hella Electronics
>
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