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I've got a project BOM costed out and I know my PCB costs. Without sending my project out for quote I'd like to be able to estimate the assembly cost by number of SMT components placed and the number of through holes (for connectors) requiring hand soldering. Assume these are assembled in the US. Assume I know the fixed costs for stencils, pick and place programming, etc.

Anybody have some ballpark figures which might help here?

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We usually have 100 units assembled at a time. I usually have a 64 to 100-pin QFP, a few 8 to 20-pin SOIC chips, and many 0805 resistors and caps.

I estimate $0.07 to $0.08 per pin/pad. That usually gets me a ballpark figure of what the assembly houses will charge. This does not include the tooling and setup charges. They run between $200 and $500, depending on the assembly house.


Edit We use assembly houses in New England (USA).

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Are you saying that at $0.07 per pin pad a QFP would cost in the order of 64 x 7c = $4.48 in manufacturing costs? So a PCB with say 1 x 64 pin QFP, 3 x 16 pin SOIC (say) and 30 0805 components would cost around 7c x (64 + 3 x 16 + 30 x 2) = 7c x 172 ~~= $12 –  Russell McMahon Feb 1 at 14:13
    
Don't forget all the 2-pin caps and resistors. Yes, each pin is roughly 7 cents in assembly costs. If you find something cheaper, post it here! –  Robert Feb 2 at 1:03
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Won't fit in a comment field, so:

Note that you say "assembled in the US" - but this would apply only if expressly stipulated, as many companies with a US front end use Asian assembly or Indian or ... . I can recommend a well priced and highly competent and conscientious assembler in Serbia and can suggest a SD, CA company who assembles in all of USA, mainland China and Taiwan.


Very much comment only:

US: $More than China to $Much more than China.
Use following as a very rough guide only.

China:

Reasonable rule of thumb is 1/3 cent US ($US0.00333 cents US) per pad or termination for SMD. Through hole fits inside that cost as long as percent through hole termination points is small compared to SMD termination points.

The above "formula" just happens to come out very roughly right in many smaller cases. It is not a true reflection of costs in extreme cases. eg 2 terminal devices such as capacitors and resistors would be costed at 2 x 0.33 cents = 2/3 cents each. An 0805 1% metal film resistor costs somewhere around 0.1 cent in manufacturing volumes so the assembly cost swamps it. Whereas an eg SOIC14 pkg would cost at 14/3 ~= 5 cents and a SOIC8 at 8/3 ~= 3 cents whereas an eg TQFP44 would cost at 44/3 ~= 15 cents. The resistor install cost may be able to be worked on and the TQFP cost, as some aspects of pick and place costings scale approximately linearly with pin count and/or package size and others are very non linear with size.

When quoted for Taiwanese manufacture via a local NZ middleman who claimed a modest markup % on costs I have had quotes for many times the cost of what can be achieved directly in mainland China.

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Thanks! This is very helpful. I just need to figure out what multiplier to use to get from China pricing to US pricing. I am doing low volume runs (50-100) so I would guess that the savings from Chinese assembly would not be very significant (if any at all). So, I can be somewhat confident that my boards are assembled here in the US. –  Jason Apr 25 '12 at 10:50
    
I'm not sure I agree with the cost per pin calculation. The cost of placing a 6 pin SOT23-6 is the same as placing a TSSOP-16. IIRC we calculated with ~2 eurocent per SMT part. But assembly cost is indeed many times the part's cost for resistors or capacitors. –  Federico Russo Apr 25 '12 at 10:54
    
@FedericoRusso - You are welcome not to agree - but you'd be disagreeing with Chinese manufacturers and not with me. This was one way that costs were calculated for real products in some cases. Elsewhere in China the basis for costing was not stated but the end priced was very close to what this yields. –  Russell McMahon Apr 25 '12 at 12:14
    
@Jason - great care! For small runs (eg 50-100) the cost can be and probably will be much higher. If you Gargoyle for: PCBA manufacture USA or PCBA assembly USA you will find many people offering services. I tried a 1000 run costing on one site for 1000 boards on a PCB that costs a few 10's of cents to make in China (manufacturing cost only) in 10,000 volume and the price was about 2 UK pounds !!! - maybe 5-15 times as high !!! –  Russell McMahon Apr 25 '12 at 12:18
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@Jason - Minimum official monthly labour rate in China is 2000 RMB or about $US350. Most people work 6 days/week for that and longish hours. Some get paid much less than official rate. Say 6/7 x 30 days x 10 hours =~ 257 hours. That's under $US1.50/hour. In US the labour rate must come from somewhere regardless of pick and place costs. Basic plastic molding in US is about 2 x China price (varies). Much same arguments re assembly apply. –  Russell McMahon Apr 25 '12 at 19:09
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There is a huge assumption that your design is even manufacturable, or that it will be possible to get high yields. QTA shops who build prototype qty's less than $5K worth need to assess all your DFT, DFM errors and assess the risks of fallout from solderability to testability. Learning curve rejections and rework costs can well exceed the BOM cost in 1st run prototypes and the NRE for screens, machine setup, ATE fixtures and process design is strongly dependant on the complexity of the design and ability for DFT to do fault isolation quickly. i.e. self test vs ICT vs FT etc. Don't be too quick to assume the cheap cost unless you can commit and prepay volumes or take a risk on low cost & cross your fingers on yield. Either they need to be desperate for business or you are willing to take huge risks on field failures.

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