Should Propeller QFN and QFP chips be made cheaper?

william chan

I noticed that surface mounted chips are usually cheaper than their DIP equivalents.

1. Is it because smd chips use less material than DIP chips since they are smaller in size?

2. Or is it because their shipping and storage costs less due to their smaller size and weight?

3. Or is it because chip suppliers know that smd customers will most likely use the chips for production, while DIP chip customers are more likely hobbyists?
If smd chips are used for production, wouldn't it mean that support costs per chip sold is much lower than DIP chips, allowing lower pricing for smd propellers?

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Leon

SMD chips tend to be cheaper to make than DIP, and are much more popular, as they are easier to assemble with automated equipment and smaller.

Parallax probably sells far more DIP chips than those in QFP and QFN packages (the main market appears to be hobbyists), so there isn't much incentive for them to reduce the prices of the latter. It's the opposite situation with most other MCUs.

Leon

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Post Edited (Leon) : 12/24/2008 2:01:22 PM GMT

Mike Green

There are clearly people who are selling products using the Propeller and some use the DIP package while others use the SMD packages. Parallax internally is probably still the largest customer for the SMD packages because of the pre-assembled boards they sell.

Leon

Mike Green said...
There are clearly people who are selling products using the Propeller and some use the DIP package while others use the SMD packages. Parallax internally is probably still the largest customer for the SMD packages because of the pre-assembled boards they sell.

I get the impression that it's very much a niche market, though, for commercial applications of the Propeller. I can't see anyone designing the DIP device into a product - it's just too big. Looking at the stock levels of the various chips, no-one seems to be using the QFN part, which is what I'd use in a commercial application. It's much better for automated assembly than QFP.

Leon

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Post Edited (Leon) : 12/24/2008 4:51:32 PM GMT

Baggers

Leon, have you seen the Hydra, that is Andre's commercial product which uses the DIP device.

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Leon

I meant products with embedded controllers. That's more of a development system.

Leon

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Phil Pilgrim (PhiPi)

For the best yields with any kind of assembly — automated or otherwise — I should think the QFP package would be preferrable to the QFN. It's just so much easier to get reliable solder joints and, perhaps just as importantly, to inspect and, if necessary, rework them. This is not to say that there aren't assembly houses just as adept at QFN assembly as with QFP assembly. But even those would prefer working with QFPs, given the choice.

The QFP is also easier to work with from a PCB layout standpoint. The reason is that the underside of the QFN has a large substrate connection which precludes any signal routing underneath the chip, which is just fine with the QFP.

The QFN package does hold a distinct advantage in size, which is a critical factor for some designs. Also, the large substrate connection may yield better thermal behavior if properly exploited for that purpose. But those are it's only advantages, as far as I can tell.

-Phil

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lynchaj

Leon said...
SMD chips tend to be cheaper to make than DIP, and are much more popular, as they are easier to assemble with automated equipment and smaller.

Parallax probably sells far more DIP chips than those in QFP and QFN packages (the main market appears to be hobbyists), so there isn't much incentive for them to reduce the prices of the latter. It's the opposite situation with most other MCUs.

Leon

Hi!· Personally, I don't mind paying a premium for the DIP packaging.· For me as a home brew hobbyist, SMT is not appealing.· Yes, it is doable but requires high quality and/or specialty soldering equipment, lots of flux paste, and steady hands.· I try to make my stuff "builder friendly" by using DIP 0.1" plated through hole technology parts.· I find those are *much* easier to work with.

I hope for the Propeller V2 that Parallax continues to support home brew hobbyists with DIP packaging.· Alternatives such as PLCC and/or DIP compatible mini boards would be OK too.· Making everything SMT is a show stopper for me.· Its just too hard to work with.· Not impossible just unpleasant.

One idea would be to make an adapter DIP miniboard with pins on the copper side which correspond to four·28 pin sockets mounted in an "H" pattern like this;

HH
HH

That'd give·112 pins which should be sufficient for QFP 100 SMT chips.

Thanks and have a nice day!
Andrew Lynch

Leon

QFN is often preferred because the chips are easier to place, and there isn't a problem with leads getting bent. It's also much better for high-speed devices and many chips are only available in QFN. I often use QFN devices on home-made PCBs and don't have any problems with them. I was thinking of designing a PCB for the QFN Propeller.

[noparse][[/noparse]Edit]

I just created the QFN footprint for the Propeller (it only took a few seconds with the Pulsonix Wizard), and updated an existing schematic of mine.

Leon

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Post Edited (Leon) : 12/24/2008 8:43:29 PM GMT

Capt. Quirk

If you look at recently released Microchip products, the Dip chips are usally cheaper, But only by .10 to .25 cents. Perhaps there is some package or technolgy·differences that support that trend.

Also the Propeller also has a certain market value, to consider.

Phil Pilgrim (PhiPi)

Leon said...
I often use QFN devices on home-made PCBs and don't have any problems with them.

Yes, but we all know from prior posts that your skills, both in fabricating and populating PCBs, border on the supernatural! Seriously, I'm sure it's an acquirable skill; but my experience with them so far has been less than satisfactory, even though QFPs don't present any problems.

-Phil

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Leon

My exploits are nothing compared with other people on the Homebrew PCB forum who do things like making multi-layer boards and modifying an ink jet printer for direct resist deposition on copper.

Leon

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Coley

Leon said...
My exploits are nothing compared with other people on the Homebrew PCB forum who do things like making multi-layer boards and modifying an ink jet printer for direct resist deposition on copper.

Got a link?

BTW I know of a commercial product here in the UK that has two propellers in it, one is a DIP and one is QFP.

Regards,

Coley

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Leon

tech.groups.yahoo.com/group/Homebrew_PCBs/

What is the reason for using both a DIP and a QFP in the same system?

Leon

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Timothy D. Swieter

In the two commercial products that I have designed with the Propeller I have used the QFP package. Mainly because size is not a concern in the product dictating a QFN and I like being able to stab at the pins. Perhaps the product in development now I could use the QFN but at the moment rev A is QFP. Also, the QFN has the pad underneath the chip which makes slightly more challenging for routing as Phil said and I am trying to stick to a two layer board.

In future products for my day job or for Brilldea I consider either the QFN or QFP to be the chip of choice and usually it is the QFP first. Now that I have my DIY reflow oven I may try the QFN as it was not something I wanted to try by hand soldering just yet though I know it is possible.

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Coley

Leon said...
What is the reason for using both a DIP and a QFP in the same system?

I don't know tbh, I never asked the designer

I would guess that as it was two distinctly seperate PCB's in the design, one were space was a constraint and the other wasn't.

The only problem with surface mount product is having boards 'in stock' usually means they are fully assembled (if you are not doing them yourself) and therefore money sat on the shelf, cashflow is king in business so unless they are fast moving sometimes DIP and thru hole is the best way to go.

Thanks for the link.... Merry Christmas to you all

Coley

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Post Edited (Coley) : 12/25/2008 1:15:17 PM GMT

Leon

I take your point about cash flow, especially for a small business. If the chip makes up a large proportion of the cost of the board, it makes sense.

I've been playing around with a single-sided proto board for the QFN device which I can make at home, and came up with this breakout pattern:

[img]http://www.leonheller.com/Designs/QFN (BO).GIF[/img]

It puts the breakout pads on 0.1" centres, like the Parallax proto board.

Timothy might be able to use something like it.

Leon

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Coley

Something like this then....




Why not go the whole hog and drop on a footprint for some decoupling caps and a crystal, would make a nice board then

Regards,

Coley

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Leon

That looks like a Microchip PIC module for their Explorer kit.

How about this:

[img]http://www.leonheller.com/Designs/Prop module.GIF[/img]

The QFN is on top and all the other parts are on the underside.

Leon

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Post Edited (Leon) : 12/25/2008 3:02:24 PM GMT

Leon

Or this:



It's 1" square!

The other parts should fit OK. There is even room for a reset button.

Leon

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Post Edited (Leon) : 12/25/2008 4:50:48 PM GMT

Timothy D. Swieter

I like these a lot Leon!!! I have in my sketch book an idea to make a little PCB assembly that is similar to the center of the Propeller Protoboard. I thought it would include the Propeller and core components (reset btn, caps, crystal) and have 0.1" centered holes in the rectangular pattern. I was thinking I would get to this in February and maybe have them up for sale on Brilldea by March. I was going to open source every portion of the design since it isn't really something to keep close.

Perhaps someone will beat me to this, but it is something I would like to do.

Merry Christmas!

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, uOLED-IOC, eProto for SunSPOT, BitScope
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