Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Delta T

Views: 3535

#68991

Delta T | 18 May, 2013

Hi guys,

Whats actually Delta T ?

As i know,its applicable for reflow profiling.

Recently my superior asked me whats the Delta T for heating settings on my reflow ? Does Delta T applicable for heater setting on my reflow ?

Pls advise as i m puzzled......

Thanks

reply »

#68999

Delta T | 20 May, 2013

Delta T usually refers to the Temperature Difference between adjoining zones in your Reflow Oven. The recommended Delta-T between heating zones is < 40 degrees C. (Less than 40 degrees C).

Here's a document that you may find helpful: http://www.ipcoutlook.org/pdf/best_practices_reflow_profiling.pdf

reply »


JAX

#69000

Delta T | 20 May, 2013

Delta T is the temperature difference between the lowest and highest temperature between measurable components at any point within the reflow process... taking into account the delay time for saturation from leading to trailing edges of the product. It is normally only mentioned when discussing peak temperatures.

reply »

#69001

Delta T | 20 May, 2013

Hi there....

Appreciate your info on this.As mentioned,the recommended delta T between heating zones is less than 40 degrees C...

Means that the Setting temperature between zones must be less than 40 deg C ?

Sorry

Thanks Rajesh Kumar

reply »


JAX

#69003

Delta T | 20 May, 2013

I don't get it...

Who cares if the zones on your oven are 10° different or 100° different, if the oven you have will support it?

The only thing that matters is the product you are building and the parameters in which you do it.

Ramp Rate, Soak time and temp (if RSS), Time to Peak, Peak Temp, Delta T, etc...

reply »

#69012

Delta T | 20 May, 2013

Well, you wouldn't want 100 deg difference from zone to zone, in that you would likely exceed your maximum ramp rate, for instance if Zone 1 was 90C and zone 2 was 190C.

Over time a general guideline (rule of thumb) has emerged, max about 40 deg difference in your heating zones. You'll arrive there by following your solder paste guidelines for the reflow profile.

For me, Delta T represents the maximum temperature difference between the hottest and coolest part of the assembly at any given moment in the reflow oven.

'hege

reply »

#69016

Delta T | 20 May, 2013

Thanks to everyone for your answers...

Delta T represents the maximum temperature difference between the hottest and coolest part of the assembly.........so if we take a profile,the hottest point would be on the solder pad and the coldest would be on an ic body.....could we calculate the temp differences between solder pad vs ic body ? If yes,the Delta T would be large......i had an argument with a customer on this......as for me the delta T should be always on solder points rather than component body.........am i right guys ?

Pleased to hear

Rajesh Kumar

reply »

#69020

Delta T | 21 May, 2013

When Delta T is measured between components on a PCB, it is recommended that the Delta T between your highest mass and lowest mass component be 4 degrees C or less.

Delta T can also be measured between zones on your reflow oven. (Delta T is defined as Temperature Difference)

This is how I interpretted your question because you associated it with "heating settings on your reflow".

reply »

#69021

Delta T | 21 May, 2013

Delta-T in reflow generally means 2 things - difference in temperature on a product or difference in temperature of your oven. Delta-T on a product is what are your hottest and coolest areas on the board. Larger parts toward the middle of the board with higher mass heat slower than smaller parts on the edges. That is one temperature difference. It also could be measured if your product is panelized, and you have multiple t-couples on the same part on different boards of the same panel. Generally the boards that are nearest the fixed real will have a slightly cooler temperature as to those on the movable rail.

The other way to measure Delta-T is on your oven. Generally you create a t-couple test board that has t-couples mounted on a plain FR-4 board or some kind of carrier. They are evenly spaced out in an X/Y pattern. Then the profile is read off of this carrier and you can see the differences on these thermocouples while running through your oven. This will show you the Delta-T of your oven. Again your fixed rail will be slightly cooler than the movable rail. Also as the front of the board enters a hotter zone the front t-couples will start to rise versus the middle and back t-couples. So all these differences are the Delta-T of your oven, which I believe your boss is looking for.

reply »

#69135

Delta T | 31 May, 2013

> Thanks to everyone for your answers... > > Delta T > represents the maximum temperature difference > between the hottest and coolest part of the > assembly.........so if we take a profile,the > hottest point would be on the solder pad and the > coldest would be on an ic body.....could we > calculate the temp differences between solder pad > vs ic body ? If yes,the Delta T would be > large......i had an argument with a customer on > this......as for me the delta T should be always > on solder points rather than component > body.........am i right guys ? > > Pleased to > hear > > Rajesh Kumar

It sounds to me like the delta T you are interested in is the temperature variance at the solder joints. You want the smallest possible difference between your joints on the small devices and the large ones. The solder joints at the larger components will tend to lag behind the smaller ones in temperature. Correct profiling and oven heating capacity are the keys. Thermocouple a large and small device joint far apart from each other as possible on the board. Profile with that concept in mind, try to match the temps (i.e. lower the Delta T). 'hege

reply »

SMT Replacement Nozzles

Large PCB Dispensing System