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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Same wave process do not apply to all finish board

Views: 3245


ING

#37119

Same wave process do not apply to all finish board | 13 October, 2005

Hi,

We have a customer who give us a 20K board contract each year. It's only thru-hole components.The baord is HASL plated. So we pass it into our wave. No problems.

Recently, our customer decided to go into GOLD PLATED finish. We take the same receipe as the HASL finish. At this time the problems begin to appear.

We get insufficient fill hole for approximatly 70% of the board. We tried to get up the preheat temperature but without any good results.

Why the flux isn't going in all the hole like before? Is there an explanation? Some tips?

There is more information about our process:

Solder temperature: 500 F Temperature of Lower preheater: 500 600 700 Temperature of Upper preheater: 600 Temprature of the Board before wave: 200 Used flux: ALPHA LONCO SLS 65C Used solder : PK METALS Flux application: Spray fluxer Wave: ELECTROVERT ULTRAPACK 350C

Feel free to ask me more info.

Thanks to all.

reply »

#37125

Same wave process do not apply to all finish board | 14 October, 2005

Hi,

What is the speed of the conveyir (contact time) and alloy: Pb free or not? Temperature of bath? Quantity of flux?

Regards

reply »


ING

#37130

Same wave process do not apply to all finish board | 14 October, 2005

For LUPO:

speed: 4.5 inch alloy: 63Sn/37Pb Solder pot temperature: 500 Quantity of flux: just to wet the board

reply »

#37132

Same wave process do not apply to all finish board | 14 October, 2005

According with temperature vs. wetting force diagram 245-250C/degrees is better, so lower temperature than 500F means better solder fill. If the speed is too lower the solder suck out form the hole. Usually 120-150cm/min. is good. (2-4s contact time) About the flux: Reason for insufficient solder fill could be flux penetration. Check the air pressure or increase the flux quantity. Usually 25-30 ug/sq. cm. You have to try different parameters - DoE is good approach.

I hope this help

Regards

reply »

#37133

Same wave process do not apply to all finish board | 14 October, 2005

Here's what I believe is happening. The main difference between the HASL boards and the gold plated boards is that HASL boards are pre-soldered. HASL boards need very little flux activity to get good hole fill and the machine settings have a wide process window. On the other hand with the gold finish all the soldering depends on your machine settings, flux activity and wetting efficiency. I would suggest turning off the top heaters making sure you increase bottom heat to compensate for the loss in top heat to reach the recommended board temp according flux spec.'s.

The reason for this is that heat has a natural rising flow, it will be easier for the flux to wick-up to the topside pad on the component side. Heating only from the bottom will increase the capillary force of the flux and the solder. The natural forces in soldering are free why not using them.

Concerning conveyor speed I've never seen excellent wave soldering results (with no-clean fluxes) at speeds higher then 3.5 ft./min.

If the above recommendations don't produce satisfactory results you might have to look for a flux with better wetting characteristics.

reply »

Mika

#37134

Same wave process do not apply to all finish board | 14 October, 2005

We have a simular problem with Ni/Au; especially whith pcb thickness more than 1.8mm. Note: These boards have been through reflow process also. 1.)Is there a maximum board thickness where it would be almost impossible to get a decent hole fil? 2.)Will the Ni/Au plating process from the pcb manufactory affect this? 3.) Will a second "heating of the board" make the wave soldering or any soldering process harder, on a Ni/Au board? Regards,

reply »

#37141

Same wave process do not apply to all finish board | 14 October, 2005

Mika,

1.) Is there a maximum board thickness where it would be almost impossible to get a decent hole fil?

Answer: The thicker the board the further the solder has to travel and the more you depend on solderability of boards and components, machine settings (physics) and flux chemistry. Not to forget hole vs. lead ratio and the amount of layers the board has.

2.) Will the Ni/Au plating process from the pcb manufactory affect this?

Answer: Poor plating quality will effect solderability. Ex. If the Au plating is too thin the exposed nickel will oxidize and will be very hard to solder. It is also important that the time between nickel plating and gold plating is as short as possible and is done by the same board house.

3) Will a second "heating of the board" make the wave soldering or any soldering process harder, on a Ni/Au board?

Answer: Au does not oxidize Ni does. If you have a good quality plating and uniform thickness a second heat cycle will not affect the solderability but on the other hand poor plating quality will seriously degrade solderability after the first heat cycle.

Hope this helps Patrick

reply »

Mika

#37145

Same wave process do not apply to all finish board | 14 October, 2005

Thanks Patrick, I our mixed standard HASL/RoHS production area; our customer have choosen Ni/Au plating for their RoHS boards. What You are saying (3.); is that we should be more attentive on the quality of the pcb manufactory. Even if our customer have made a very sharp specification of the pcb; it is No guarantee that this will be fulfilled by the pcb manufactory. Right? How to achieve this? We have previously sent pcb:s to a lab for testing of "almost everything" and found out that the pcb:s meet the specs. But hey, things change so we might need to do this agian. Sincerly,

reply »

#37147

Same wave process do not apply to all finish board | 14 October, 2005

Mika,

If I understand you correctly you compare hole fill of Ni/Au plated boards in a lead-free process with HASL 63/37 boards soldered with leaded solder. If this is the case you might be facing the challenges in Pb free wave soldering with the limited wetting characteristics of lead-free alloys compared to leaded alloys.

reply »

Mika

#37157

Same wave process do not apply to all finish board | 14 October, 2005

Thanks Patrick for the replay, No, we do not mix the alloys nor Pb pcb:s/RoHS pcb:s in the case I described. It is simply as this: With both the different soldering processes we facing this phenomenon; but whith the RoHS SN100 or SAC305 it turns out even worse. I am not sure, but maybe I should start a new thread?

How about [barry] did he got the answer on the original question he is looking for? Please let us know, beacause that is the essentially of this forum. Sincerly,

reply »

Mika

#37158

Same wave process do not apply to all finish board | 14 October, 2005

I Am SORRY; I mean of corse ING. I must be tired, because I start mix one author whith the next one. Just imagine what I will do with the alloys :-) Sincerly,

reply »


ING

#37173

Same wave process do not apply to all finish board | 17 October, 2005

Thanks Patrick.

I understand your points. It gives us good results. I didn't know about the flux activity on Gold finish. It's a pleasure to get this kind of explanantion.

reply »

KEN

#37199

Same wave process do not apply to all finish board | 18 October, 2005

I suspect the problem is a surfactant issue in your flux. I have seen where boards are fluxed, hit the solder fountain and come out like they never touched the solder. There was an inadequate surfactant between the solder and the PCB.

I know you don't want to hear this but not all fluxes work well on all surface finishes.

reply »

Plasma prior Conformal Coating

Real-time PCB X-ray Inspection System