Home > SMT Assembly News

Solder Skips on a Printed Circuit Board-WAVE SOLDERING DEFECTS

Unsoldered surface mount joints are referred to as solder skips where the termination does not have any solder. It is caused by incorrect chip wave height or gassing of the flux on the underside of the board.

As Figure 1 shows, the resist thickness can also cause the problem or make it worse. Solder resist or mask should be level with the pad surface or below it for the ideal assembly conditions. If the mask is thick it creates a cavity around the pad where flux vapours are trapped forming a bubble. The solder cannot displace the vapour easily to form a joint.

Figure 1: Resist thickness contributed to this solder skip
Figure 1: Resist thickness contributed to this solder skip.

While any surface mount solder joint not wetted with solder is generally referred to as a solder skip, some people refer to these as insufficient solder joints, which is misleading.

During assessment of the problem, it is important to check if a fresh coating of solder is on the pad or on the component termination. Often, the presence or lack of a new solder coating on the leads can indicate the root cause of the problem.

The most common causes of skipping are incorrect chip wave height, gassing of flux under the board surface or excess resist thickness. Each of these faults can be easily fixed, although the resist may take a little longer if you have a large stock of boards, but review your PCB specification.

In Figure 2, adhesive has contaminated the pad surface. Although no adhesive deposit is visible, some adhesives allow an invisible film to bleed out from the dot area during curing. Try evaluating your adhesive.

Figure 2: Adhesive contamination on the pad surface caused this solder skip
Figure 2: Adhesive contamination on the pad surface caused this solder skip.

The example in Figure 3 is clearly not soldered, and the waves could not have been that badly adjusted in a professional company, could they? It is more likely that the board was not correctly positioned in the finger conveyor or in the pallet. The pallets may be distorted or the clips are not holding the board flat.

Figure 3: PCB not correctly positioned on the finger conveyor or in the pallet
Figure 3: It is likely that the board was not correctly positioned on the finger conveyor or in the pallet.


SMT Reflow Oven, Lead free Reflow Oven, Reflow Oven Manufacturer, LED reflow oven, PCB Reflow Oven, Nitrogen Reflow Oven, Dual Rail Reflow Oven, China Reflow Oven, wave soldering machine, Dual Rail Wave Soldering Machine, Nitrogen Wave Soldering Machine, Wave Soldering Machine Manufacturer.

Flason Electronic Co.,ltd provide a full SMT assembly line solutions, including SMT Reflow OvenWave Soldering MachinePick and Place MachineSMT Stencil PrinterSMT AOI SPI MachineSMT Reflow OvenSMT Peripheral EquipmentSMT Assembly lineSMT Spare Parts  etc any kind SMT machines you may need, please contact us for more information: wechat whatsapp:+8613691605420, Skype: flasonsmt, Email: sales@flason-smt.com
1) This is the first time I use this kind of machine, is it easy to operate?
There is English manual or guide video that show you how to use machine.
If you still have any question, please contact us by e-mail / skype/ phone /trademanager online service.
2) If machine have any problem after I receive it, how can I do ?
Free parts send to you in machine warranty period.
If the part is less than 0.5KG, we pay the postage.
If it exceeds 0.5KG, you need to pay the postage.
3) MOQ ?
1 set machine, mixed order is also welcomed.
4) How can I buy this machine from you? ( Very easy and flexible !)
A. Consult us about this product on line or by e-mail.
B. Negotiate and confirm the final price , shipping , payment methods and other terms.
C. Send you the proforma invoice and confirm your order.
D. Make the payment according to the method put on proforma invoice.
E. We prepare for your order in terms of the proforma invoice after confirming your full payment.
And 100% quality check before shipping.
F.Send your order by air or by sea.
5)Why choose us ?
A. Gold supplier on Alibaba !
B. Trade assurance to US$54,000 !
C. Best price & Best shipping & Best service !


Contact: Mr Tommy

Phone: +86 13691605420

Tel: +86 -755-85225569

Email: sales@flason-smt.com

Add: No.94,Guangtian Road,Songgang Street,Bao an District Shenzhen China